2021 | 74/3 | 273–286 | 11 Figs. | 1 Tab. | Appendix | www.geologia-croatica.hr Journal of the Croatian Geological Survey and the Croatian Geological Society 1. INTRODUCTION Caves are natural underground voids formed predominantly by the dissolution of soluble (mostly carbonate) bedrock and they act as natural windows to the Earth’s Critical Zone (ECZ). The ECZ is a relatively thin, but extremely heterogeneous zone that extends from the bottom of the groundwater body to the uppermost parts of the surface vegetation in which life can be sustained by cou- pled chemical, biological, physical and geological processes (BRANTLEY et al., 2007) and which is most exposed to envi- ronmental changes. The natural functioning of this system is strongly regulated by climate and associated hydrological and vegetational changes which can be reliably archived within spe- leothems (REGATTIERI et al., 2019). Therefore, speleothem- based research is increasing globally (COMAS-BRU et al., 2020), complemented by the monitoring of cave properties such as hy- drogeology, hydrogeochemistry, microclimate, cave air composi- tion, etc., the understanding of which is essential for the appro- priate interpretation of the palaeoenvironmental signals recorded in spelean carbonate. Although it is just a trace gas in the atmosphere (416.49 ppm in May 2021, NOAA accessed on 30 August 2021), CO2 plays an important role in the overall Earth system, especially when mis- balanced from the natural state. On an incomparably smaller Spatio-temporal variations of cave-air CO2 concentrations in two Croatian show caves: natural vs. anthropogenic controls Maša Surić*, Robert, Lončarić, Matea Kulišić and Lukrecija Sršen University of Zadar, Department of Geography, Ul. dr. F. Tuđmana 24, 23000 Zadar, Croatia; (*msuric@unizd.hr) doi: 10.4154/gc.2021.21 Abstract Carbon dioxide (CO2) concentration (CDC) plays an important role in karst processes, govern- ing both carbonate deposition and dissolution, affecting not only natural processes, but also hu- man activities in caves adapted for tourism. Its variations due to various controlling parameters was observed from 2017 to 2021 in two Croatian show caves (Manita peć and Modrič) where we examined inter- and within-cave correlation of internal aerology regarding the sources, sinks and transport mechanism of CDC in a karst conduit setting. In both caves, the main sources of CO2 are: i) plant and microbial activity i.e. root respiration and organic matter decay within soil horizons and fractured epikarst, and ii) degassing from CO2-rich percolation water. The main sink of CO2 is dilution with outside air due to cave ventilation. Chimney-effect driven ventilation controlled by seasonal differences between surface and cave air temperatures shows winter (ToutTcave ) ventilation regime, which are modulated by the geometry of cave passages, the transmissivity of the overlying epikarst, and occasionally by the external winds, especially the gusty north-eastern bora wind. In these terms, the Modrič Cave appears to be more confined and less ventilated, with a substantial CDC difference between the left (550- 7200 ppm) and right (1475- >10,000 ppm) passages. The Manita peć Cave is, in contrast, ven- tilated almost year-round, having 7 months of CDC equilibrated with the outside atmosphere and the highest summer CDC values of ~1415 ppm. In both caves, at the current level of tourist use, anthropogenic CO2 flux is not a matter of concern for cave conservation. In turn, in the innermost part of the right Modrič Cave passage visitors’ health might be compromised, but the tourists are allowed only in the left passage. Speleothem growth rate, recognized as a useful palaeoenvironmental proxy for speleothem- based palaeoclimate studies, strongly depends on CDC variations, so the high CDCs recorded in the Modrič Cave indicate the potential periods with no speleothem deposition due to the ham- pered degassing of CO2 from the dripping groundwater. The opposite effect i.e. enhanced ven- tilation (that supports calcite precipitation) during the windy glacials/stadials, as well as substan- tial vegetational changes must also be taken into consideration when interpreting environmental records from spelean calcite. scale, CO2 in cave air is, in an underground environment, also important and interesting for its various sources, sinks and effects that occur with or without human interaction. Generally, CO2 partial pressure is one of the most important factors that controls both carbonate dissolution and speleothem deposition (DREY- BRODT, 1999) and the understanding of CO2 distribution and dynamics in the underground is essential for various aspects of cave science including the aforementioned speleothem-based pa- laeoclimate studies (BALDINI et al., 2008; COWAN et al., 2013; GREGORIČ et al., 2013). Cave air CO2 concentration (CDC) is controlled by dynamic equilibrium between different CO2 sources and sinks and their competing influences depending on both spa- tial and temporal particularities of the cave environment. The main natural sources of underground CO2 are: i) diffusion of CO2-rich air generated by root respiration and organic matter de- cay transmitted from the soil through the joints and fissures, ii) degassing from the groundwater which was enriched by CO2 on its way through the soil and epikarst, iii) biological productivity i.e. decomposition (micro-organisms feeding on organic matter, usually guano) within the cave, and iv) deep-seated (thermal) geogenic sources (BALDINI et al., 2008; FAIRCHILD & BAKER, 2012; PRELOVŠEK et al., 2018). In addition to the aforementioned natural sources, show caves may receive extra Article history: Manuscript received May 27, 2021 Revised manuscript accepted September 16, 2021 Available online October 27, 2021 Keywords: show cave, CO2, cave ventilation, anthropogenic impact, Croatia G eo lo gi a C ro at ic a 274 Geologia Croatica 74/3 anthropogenic CO2-flux from visitors breathing (e.g. DRAGO- VICH & GROSE, 1990; LIÑÁN et al., 2008). The most substantial sinks of cave air CO2 are: i) ventilation i.e. dilution of the CO2- rich cave air with relatively CO2-poor outside air, and ii) uptake by groundwater i.e. CO2 dissolution in under-saturated cave wa- ter (COWAN et al., 2013). Elevated cave air CDC, increased either naturally or anthro- pogenically, may affect the cave environment in several ways. First, when percolating groundwater (in which CO2 is controlled predominantly by soil pCO2) reaches the air-filled voids, equili- bration with lower pCO2 cave air occurs and degassing of CO2 can cause calcite precipitation from the water saturated with re- spect to calcite (HOUILLON et al., 2017). However, elevated pCO2 in cave air can hamper degassing of CO2 from the dripping groundwater resulting in either the absence or cessation of calcite deposition (BALDINI et al., 2006; 2008). Second, cave air CO2 dissolved in water condensed within the cave produces carbonic acid which may dissolve bedrock or already crystallized spelean calcite, a process known as condensation corrosion (DUBLYAN- SKY & DUBLYANSKY, 1998; FAIMON et al., 2006; BALDINI et al., 2006; GABROVŠEK et al., 2010). Thirdly, high cave air CDC values are related to health issues, so already a CDC of 5000 ppm is regarded as the occupational exposure limit (ILO, 2006), and it must be considered for all visitors in show caves, including tourists, guides, cavers and scientists. The majority of caves have elevated CDCs, usually in summer, which in some cases reach extremely high values, such as ~14,000 ppm in the Romanian Urșilor Cave (CONSTANTIN et al., 2021), ~22,000 ppm in Gale- ria das Lâminas, Portugal (BENSON et al., 2021), ~35,000 ppm in Béke Cave, Hungary (CZUPPON et al., 2018), ~31,000 ppm in District Park Cave and ~38,000 ppm in Natural Bridge Caverns in the USA (COWAN et al., 2013), even up to >44,000 in Chauvet Cave (BOURGES et al., 2020) and ~60,000 ppm in Causse d’Aumelas (BATIOT-GUILHE et al., 2007) in France. In Croatia, the first records of elevated CDC were published by MALEZ (1954) and BOŽIČEVIĆ (1966), and afterwards numerous occur- rences of high CDC have been reported by cavers, but systematic monitoring began only in 2016 within 5 show caves in the conti- nental part of Croatia (BOČIĆ & BUZJAK, 2018). Here, we present the first results of multi-year monitoring of the cave environment aimed at estimating spatial and temporal variations of cave air CDC in two show caves located in the coastal zone of the Dinaric karst in Croatia – the Manita peć and Modrič caves, both considered to be small and simple caves with relatively low numbers of visitors. The obtained data sets enabled us to: i) reveal cave ventilation dynamics in order to detect pos- sible seasonal speleothem growth patterns crucial for palaeoen- vironmental studies; ii) estimate the anthropogenic contribution to the cave CO2 background levels and potential effects on the cave interior, and iii) assess the possible health hazard for the visitors from an elevated CDC. 2. STUDY SITE The Dinaric karst in Croatia is characterized by relatively high mountain ranges (up to 1831 m) stretching parallel to the coast, one of which is Velebit Mountain – the host of the two studied caves. Modrič Cave is located in its foothill at 32 m a.s.l., while the entrance of Manita peć Cave is at 570 m a.s.l., on the side of the canyon perpendicular to the mountain range (Fig. 1). Given their geographical position and geological settings, some specific meteorological features (e.g. bora events) are expected to influ- ence the cave atmospheres i.e. ventilation. The Modrič Cave (44° 15’ N, 15° 32’ E) is situated 120 m from the shoreline on the SW slope of the central part of Velebit Mountain. The cave is formed within a 2.5 km wide fault zone, in well-bedded Upper Cretaceous limestone (MIKO et al., 2002), and consists of two, mostly horizontal, passages with a total length of 829 m and a single narrow entrance (KUHTA et al., 1999). Overlying bedrock is 1-27 m thick and vegetation cover above the cave is sparse trees, bush and grassland. Soon after its discovery in 1985 and an initial topographic survey, Modrič Cave came to the attention of various scientific disciplines and has since become one of the most investigated Croatian caves (SURIĆ, 2018). Palaeontological research of Quaternary verte- brate faunal remnants (MALEZ, 1987; AGUILAR et al., 2004) was followed by a thorough speleological and geological survey and partial geochemical and hydrogeological investigations (KUHTA et al., 1999); the geochemical aspect was focused on sediments, percolating water and bat guano influences (MIKO et al., 2001; 2002). Because the cave has been open for adventure tourism since 2004, radon activity in the cave air was occasion- ally monitored (BUZJAK et al., 2010; SRŠEN, 2019). For the pur- pose of palaeoclimate reconstruction, thorough microclimate monitoring, along with speleothem and dripwater stable isotope analyses, were conducted in several campaigns from 2003 on- wards (SURIĆ et al., 2010; 2017; 2020; RUDZKA et al., 2012). The Manita peć Cave (44°18’ N, 15°28’ E) is located on the steep flank of the Velika Paklenica canyon carved perpendicularly into the Velebit Mountain. It is a simple, 175 m long, descending spacious chamber formed in Upper Jurassic limestone, with a height up to 38.5 m and total volume of 67,510 m3 (KUHTA, 2010). The overburden is up to 80 m thick and heavily fractured. Ground surface cover is sparse patches of terra rossa, shrubs and grass. Scientific interest for this cave had already begun in 1900 with the first biospeleological investigation, followed by geological and speleological surveys in 1929, which also included preliminary notes on its microclimate and hydrogeology. Due to its rich spe- leothem formations, in 1937 it was adapted for visitors with con- struction of the first pathway and a new artificial entrance (Action Plans National Park Paklenica, 2007). In the following decades the cave has been the site of occasional environmental research projects, one of which was the monitoring of radon activity in the cave atmosphere (RADOLIĆ et al., 2012). This was fundamental for assessing the health and safety of visitors and guides. Although both caves are open for visitors, there is a signifi- cant difference in the approach to touristic management between them. Modrič Cave is available for individually arranged visits year-round, but the peak numbers of visitors occurs between April and October, with an annual maximum of 727 visitors in 2019. Organized as an adventure tour with caving equipment, visitors in groups of up to 30 people spend approximately 1.5 to 2 hours within the left passage of the Modrič Cave. Manita peć Cave operates as a “classical” show cave with guided tours and no need for special equipment. According to the current timeta- ble, during the summer (July, August, September), Manita peć Cave is open every day, then three days a week through the late spring and early autumn (May, June, October), finally in April only one day per week. It is closed for visitors during the winter season, except for organized groups on demand. In order to min- imize anthropogenic impact, it has been open just for three hours per day, except during 2017-2018 when it was open for 4 hours per day. A maximum of ~13,000 visitors per year was reached in 2017. The usual visiting time in Manita peć Cave is up to 30 minu- tes for groups of 25-30 visitors. G eologia C roatica 275Surić et al.: Spatio-temporal variations of cave-air CO2 concentrations in two Croatian show caves: natural vs. anthropogenic controls 3. METHODS Monitoring of cave air CDC was conducted in Modrič Cave from March 2017 to March 2021 in the right passage and from July 2018 to March 2021 in the left passage. In Manita peć Cave CDC monitoring covered the period between January 2018 and March 2021. Measurements were performed on a monthly basis using a 7755 AZ Handheld CO2 & Temperature & Relative Humidity Meter (CO2 range 0-9999 ppm; resolution 1 ppm; accuracy ±50 ppm or ±5% of reading (0-2000 ppm); air temperature range -10-60 °C; resolution 0.1 °C; accuracy ±0.6 °C). The measurements were carried out at the beginning of each month, on the same day in both caves. Along with regular monthly monitoring, CDC was measured on several occasions before and after tourist group vis- its (usually 20-30 people) in spring and summer, to assess anthro- pogenic impact on the cave air properties. Eight measurement points were established in Manita peć Cave, and 7 in Modrič Cave, distributed at approximately even distances from the en- trance to the innermost parts, with additional measurement points in front of each cave (Figs. 1c &1d). Additionally, in the Modrič Cave’s right passage, air tem- perature and relative humidity were also continuously recorded (1-hour intervals) using Onset Hobo® PRO-V2 U23-001 data log- gers (T range -40 to 70 °C; accuracy ±0.25 °C from -40 to 0 °C; ±0.2 °C from 0 to 70 °C; resolution 0.04 °C; RH range 0 to 100%, accuracy ±2.5% from 10% to 90% RH, ±5% <10% or >90% RH, resolution 0.05%). External temperatures and precipitation data were obtained from the Croatian Meteorological and Hydrologi- cal Service (CMHS) for the station in Starigrad Paklenica (ca. 4 km SW from Manita peć Cave and ca. 9 km NW from Modrič Cave). However, due to the station’s technical failure, from De- cember 2018 onwards, data for the station in Novigrad (ca. 16.5 Figure 1. Study area with cave locations and basic climatic data for the meteorological station in Starigrad Paklenica (ca. 4 km SW of the Manita peć Cave and ca. 9 km NW of the Modrič Cave) for 1992-2018: a) air temperature and precipitation; b) difference between precipitation and potential evapotranspiration (Croatian Meteorological and Hydrological Service /CMHS/, 2021); c) east-facing entrance of Manita peć Cave and the plan with measurement points; d) north-facing en- trance of Modrič Cave and the plan with measurement points. Water balance (potential evapotranspiration) was calculated using the Thornthwaite evapotranspi- ration model (THORNTHWAITE, 1948; MCCABE & MARKSTROM, 2007). G eo lo gi a C ro at ic a 276 Geologia Croatica 74/3 km SE from Manita peć Cave and ca. 8 km S from the Modrič Cave) was used instead. Both stations share similar topographic location and climate properties, so no significant changes in data representativeness are expected. 4. RESULTS 4.1. Spatio-temporal variations of the cave air CO2 concentration Spatial and temporal variations of Modrič Cave air CDC are pre- sented in Fig. 2 and the complete data set is provided in Tab. 1A in the Appendix. At the first measurement point M00 in front of the cave, during the period between March 2017 and March 2021 we recorded CDCs from 350 ppm to 590 ppm. Cave air CDC of the main passage measured at points M11 and M22 varied be- tween 412 ppm and 6868 ppm; similar to that in the left passage, values between 480 ppm and 7228 ppm were recorded at points T13, T14 and T15. Meanwhile, along the right passage, at mea- surement points M31 and M32, the CDC range was from 994 ppm to >10,000 ppm (i.e it exceeded the measurement limit of instru- ment). Spatio-temporal variations of cave air CDC in the Manita peć Cave between January 2018 and March 2021 are given in Fig. 3 and in Tab. A2 in the Appendix. The first measurement point (MP 01) was ~100 m away from the cave entrance at the most exposed part of the mountain slope, at the lookout, and provides values of the outside CDC, while point MP 02 was at the very entrance of the cave, right in front of the gate bars with a CDC range of 339-664 ppm (Fig. 4). The remaining measurement points (MP 03 – MP 09), which were distributed evenly along the descending channel, had CDC values ranging between 325 ppm and 1415 ppm. Temporal variations of CDC in both caves are seasonal, with the highest values in summer/autumn, and the lowest during the winter/spring, which is the opposite of natural atmospheric CDC fluctuations (Pearman & Hyson, 1981). Namely, due to the phy- toplankton bloom and plant photosynthesis in the warmer part of Figure 2. Variation of CO2 concentrations along a) the left passage (July 2018 - March 2021) and b) the right passage (March 2017 - March 2021) of the Modrič Cave. Note that both plots contain the same values for the first three measurement points, i.e. exterior point M00 and main passages’ points M11 and M22. Figure 3. Variation of CO2 concentration in the Manita peć Cave (January 2018 – March 2021). G eologia C roatica 277Surić et al.: Spatio-temporal variations of cave-air CO2 concentrations in two Croatian show caves: natural vs. anthropogenic controls the year, CO2 is absorbed from the atmosphere, so the CDC in the northern hemisphere decreases, while in autumn decaying plants release their CO2 back into the atmosphere, which along with elevated fossil fuel consumption leads to an atmospheric CDC increase. Surprisingly, the CDC variations in the surface air in front of our studied caves at M00 and MP 01 do not follow that pattern. Instead, they coincide with in-cave CDC variations, as demonstrated in Fig. 4, showing the influence of the in-cave environment on the nearest surroundings. 4.2. Visitor numbers and their impact on cave air CO2 concentration The total annual numbers of visitors in the caves are given in Figs. 5a and 5c, and the monthly distribution of the Manita peć Cave visitors is presented in Fig. 5b. The highest annual values reached in 2017 and 2018 are due to the prolonged working hours (4 hours per day instead of 3 hours) of Manita peć Cave, and the sudden decrease of visitor numbers in both caves is a direct response to the COVID-19 pandemic. Measurements of CDC before and after groups of tourists were conducted in spring and summer season at the sites where the visitors pause for the sightseeing or explanations, and the re- sults are given in Table 1. During the spring season, the increase of CDC measured immediately after the groups was 14-22% and 20-28% for Manita peć Cave and Modrič Cave, respectively. However, due to the relatively low initial CDC, absolute values after the visitors are still within safety limits. High CDCs in the summer season remained after the visitors at similar levels, ~1250 ppm in Manita peć Cave and ~5100 ppm along the left passage of Modrič Cave. The exception was measurement point MP03 in Manita peć Cave with an increase of 66% (from 740 ppm to 1230 ppm), but due to its location near the entrance, the CDC probably quickly reduced to the previous values. 5. DISCUSSION Distribution and variations of cave CO2 are controlled by an in- terplay of different sources and sinks and their spatial and tem- poral evolution, which are in the case of Modrič and Manita peć caves, relatively simple. There are no underground rivers or geo- genic sources of CO2, and in-cave decomposition of organic mat- ter does not play an important role, since there are no large de- Figure 4. Variation of air CO2 concentration in the vicinity of the cave entrances; measurement point M00 was several metres in front of the Modrič Cave, MP 01 was at the lookout ~100 m away from Manita peć Cave and MP 02 was at the very gate of the same cave. Note the relatively invariant MP 01 values in relation to the covariance of M00 and MP 02. Figure 5. Number of visitors a) annually in Manita peć Cave (2005-2020); b) monthly distribution in Manita peć Cave, and c) annually in Modrič Cave (2012- 2020). Note the significantly different y-axes scales in a and c. Sudden decrease of number of visitors in 2020 reflects the COVID-19 pandemic. (Sources: NP Pa- klenica for Manita peć Cave and M. Buzov, pers. comm. for Modrič Cave). Table 1. Effect of groups of visitors on air CO2 concentration (in ppm) measured before and immediately after the visitor groups in Manita peć Cave and in the left passage of the Modrič Cave, in spring and summer seasons. Only locations with longer tourists’ residence time are considered. For measurement points, see Fig. 1. Modrič Cave Measurement point 6 April 2018 20 July 2018 Before After Before After M11 5169 5178 M22 588 705 5132 5172 T13 575 715 5068 5158 T14 594 761 5034 5044 Manita peć Cave Measurement point 1 May 2018 1 August 2018 Before After Before After MP03 452 577 740 1230 MP04 524 600 1243 1246 MP05 505 614 1270 1257 MP06 512 607 1259 1267 MP07 510 602 1315 1317 MP08 502 612 1346 1313 G eo lo gi a C ro at ic a 278 Geologia Croatica 74/3 posits of organic matter such as guano. The main factors controlling CDC are transport of CO2-rich air from the soil ho- rizon and epikarst, along with CO2 degassing from drip water, and its dilution by the external CO2-poor air, i.e. cave ventilation (EK & GEWELT, 1985). Cave ventilation dynamics follow seve- ral patterns controlled predominantly by seasonal temperature variations, cave morphology, and potentially by anthropogenic CO2-flux, while the ventilation itself is mainly triggered by dif- ferences between outside (Tout) and cave air (Tcave) temperatures (SPÖTL et al., 2005; BALDINI et al., 2006), and wind (RIECH- ELMANN et al., 2019; KUKULJAN et al., 2021). These particu- lar features are discussed bellow. 5.1. Impact of cave morphology and epikarst structure on spatial CDC variations Substantial differences between the Modrič and Manita peć cave morphology are depicted in their cross sections (Fig. 6). Modrič Cave is almost horizontal except for the small descent near the entrance, and a short ascent at the beginning of the right passage. Although relatively similar in dimensions, the two passages dif- fer by their accessibility. Along the left passage during the winter time, there are only small variations of CDC, with values <100 ppm higher that those outside the cave (Fig. 7a). Similarly, CDC values are also relatively evenly distributed in the summer-au- tumn season (Fig. 7b), which is likely caused by unobstructed movement of the air through the left passage due to its larger di- mensions compared to the right one. In the right passage, CDCs are substantially higher both during the warm and cold seasons, and spatial variations are more pronounced. The entrance section of the right passage (after M22) is only slightly ascending, but obviously enough to prevent or at least mitigate the inflow of the cool outside air during the cold season. Additionally, the more diverse morphology of the right passage with several smaller chambers connected by narrow corridors makes this passage more constrained. An abrupt increase in CDC occurs ca. 50 m inside the passage, which is in accordance with the findings of BALDINI et al. (2006) and MILANOLO & GABROVŠEK (2009) who generally recorded such sudden increases in CDC right after constrictions in their studied caves. There is another difference in the spatial distribution of CDC between the two passages in the Modrič Cave. The left one has evenly distributed either summer (higher) or winter (lower) CDC values throughout the whole passage, while in the right passage the CDC values increase towards the end (Fig. 7). This partially reflects the structure of the overlying bedrock, which is appar- ently more fractured, and hence easily ventilated, due to the fault zone along the left passage. The sets of small stalactites and soda- straws in the second part of this passage additionally point to the matrix porosity (FAIRCHILD & BAKER, 2012) of that part of the cave and can be regarded as a macrofissural network cf. BOURGES et al. (2006), defined as fissures of less than 1 mm aperture which transfer both rainwater and CO2-rich soil air to- wards the cave. Conversely, the bedrock of the right passage is more compact, or maybe even sealed by the spelean carbonate which is also reflected in more homogenous drip rates, sometimes unresponsive to surface rain events (SURIĆ et al., 2018). The ap- parent differences of the atmospheric regimes in the relatively similar passages underline that the volume of the critical zone involved in the control of in-cave atmosphere is much larger than the volume of the underground chambers and includes also the voids of the surrounding karstified bedrock (BOURGES et al., 2006). On the other hand, the Manita peć Cave consists of one large descending chamber that begins with two relatively large open- ings (1.7×2.5 m and 1.3×2.0 m), and the height difference from the entrances to the lowest point of the cave is 35 m. In addition, heavily fractured overlying bedrock detected in some places by the immediate rain fracture-flow infiltration (SURIĆ et al., 2017), Figure 6. Cross section of Modrič and Manita peć caves with marked measurement points. Figure 7. Spatial distribution of cave air CO2 concentration in Modrič Cave passages during the: a) winter season – measured 1 February 2021; b) summer season – measured 3 September 2019. G eologia C roatica 279Surić et al.: Spatio-temporal variations of cave-air CO2 concentrations in two Croatian show caves: natural vs. anthropogenic controls enables considerable air circulation via epikarst. Given the ful- filled prerequisites for significant ventilation, the spatial varia- tions of CDC remain relatively minimal, particularly during the winter when cold air descends into the cave and CDC values within the cave are practically equal to the external ones (Fig. 8a). Summer spatial CDC variations are also relatively small (the maximum recorded value was 1415 ppm), specifically when com- pared to those in Modrič Cave. For the summer CO2 distribution, the vertical dimension of the cave plays the leading role, with the inflow of the outside air being obstructed by the cold and dense air trapped at the cave bottom. This phenomenon has already been identified in the Manita peć Cave by the pocket of cold air having a year-round stable temperature of 9.0 °C (1σ=0.4 °C), while the external mean annual air temperature (MAAT) in front of the cave was 13.7 °C (2014-2015) (SURIĆ et al., 2017). Such a stable thermal stratification during warm periods in aerodynami- cally closed cold trap systems has been discussed in e.g. BOURGES et al. (2006), LUETSCHER et al. (2008), MILAN- OLO & GABROVŠEK (2009) etc. 5.2. Temporal controls of the cave air CO2 concentration Temporal variations of CDC given in Tabs. A1 and A2 and pre- sented in Figs. 2 and 3 point to the strong seasonal mode in both studied caves. Given the constant air cave temperature, during the warm season the cave air temperature is lower than outside, and during the cold season the situation is the opposite. Correla- tion between ΔT (Tout – Tcave) and CDC implies that air tempera- ture differences govern the air density gradients between the out- side and cave air and also control air exchange i.e. ventilation (FAIRCHILD & BAKER, 2012). Studies conducted in caves with a comparable temperature regime and morphology in Germany (Bunker Cave; RIECHELMANN et al., 2019), Puerto Rico (Cueva Larga; VIETEN et al., 2016) and Bosnia and Herzegovina (Srednja Bijambarska Cave; MILANOLO & GABROVŠEK, 2009) revealed the same driving mechanism of seasonal CDC variations; that is ventilation driven by an air density gradient between external and cave air. Such circulation is known as a chimney effect, usually ascribed to the caves with two or more entrances at different altitudes (FAIRCHILD & BAKER, 2012). During the summer, warm surface air enters the cave via an up- per entrance, cools down and with increased density it descends and emerges at a lower entrance as cold cave air. In winter time, cold dense outside air inflows through the lower entrance, warms up and, because it is less dense, appears at the upper opening (SPÖTL et al., 2005). Despite the fact that our studied caves have only one passable entrance, the chimney effect can be attributed to them, particularly to the Modrič Cave since it has only 2-30 m overburden thickness of faulted and heavily fractured limestone bedrock, which practically acts as an upper entrance. Therefore, we identified two ventilation regimes and associated CDC varia- tion patterns: – summer: with Tout>Tcave – warm surface air on its way through the epikarst is enriched by CO2, downdraft occurs and cool cave air flows outwards from the caves, as proven by mea- sured elevated CDC in front of the caves (Fig. 4). – winter: with ToutTcave and Tout10,000 ppm) were recorded during the late summer of 2019 which was the coolest summer between 2017–2020, but the long- lasting warmth with above-average precipitation in July (CMHS, 2021) obviously triggered intensive biological activity inducing the CDC increase. The aforementioned impact of different morphology of the left and right passage in the Modrič Cave is also evident when considering temporal variations in CDC distribution. Namely, the sudden drop in CDC values recorded in the left passage during the autumn/winter transition period (e.g. November and Decem- ber 2018) with CDC values decreasing from >5000 ppm to 500-600 ppm (Fig. 9 & Tab. A1) coincides with the drop of the Figure 8. Spatial distribution of cave air CO2 concentration in Manita peć Cave during the: a) winter season – measured on 1 February 2021; b) summer season – measured on 3 September 2019. G eo lo gi a C ro at ic a 280 Geologia Croatica 74/3 Tout below Tcave, which usually occurs during October and Novem- ber and triggers the inflow of the CO2-poor outside air into the cave. At the same time, the decrease of the CDC in the right passage is much smoother as values drop from ca. 5000-6000 ppm to 3000- 4500 ppm owing to the right passage’s tight spots preventing the rapid inflow of cooler outside air, but also because of apparently more compact bedrock and therefore reduced outflow. The transition between higher summer and lower winter CDC values in the Manita peć Cave (Fig. 10) is governed by both the chimney effect and the cold trap responsible for the cave’s site-specific temperature regime. The cold trap is present during most of the year, so Tout remains below Tcave only relatively briefly during the winter (December to February/March). Still, the in- nermost part of the cave retains unchanged CDC until May/June when Tout increases to approximately 15-17 °C (Fig. 10). Presuma- bly, because of the large volume of that part of the cave (cave ceiling is ca. 30 m high), it takes a longer time for the CDC to increase. Also, the surface above the cave is over 600 m a.s.l., so increased biological activity in the soil lags behind that on the surface above the Modrič Cave. 5.3. Impact of specific meteorological events Occasionally, ventilation can be further modulated, and more rapid changes in CDC values are expected during specific me- teorological episodes such as strong winds (RIECHELMANN et al., 2019; KUKULJAN et al., 2021) and intense precipitation events (BOURGES et al., 2020). Modrič and Manita peć caves have northward- and eastward-facing entrances, respectively, ex- posed to the north-eastern bora – a gusty downslope windstorm characteristic for the eastern Adriatic coast (GRISOGONO & Figure 9. Time series of the surface (Tout) and cave air temperature (Tcave) and air CO2 concentration at M32 – the innermost measurement point within the right passage where the highest CDC values were recorded, never falling below 1450 ppm. Surface temperature is compiled from the Starigrad (1/2017-7/2018) and Novigrad stations (8/2018-8/2020), equally distant from Modrič Cave. Data for April 2020 are missing due to the COVID-19 pandemic. Figure 10. Time series of the surface (Tout) recorded in front of the Manita peć Cave, and air CO2 concentration at MP09 - the innermost measurement point where the highest CDC values were recorded. Cave air temperature (Tcave) is an average value recorded between 7/2012 and 7/2014. Note the significantly shorter dura- tion of Tout < Tcave than Tout > Tcave. Data for October 2018 are missing due to device failure, for April 2020 due to the COVID-19 pandemic, and for June 2020 due to the drowning of the innermost part by the extreme rainfall. G eologia C roatica 281Surić et al.: Spatio-temporal variations of cave-air CO2 concentrations in two Croatian show caves: natural vs. anthropogenic controls BELUŠIĆ, 2009). During the bora episodes, which are particu- larly frequent in March (e.g. IVANČAN-PICEK & VUČETIĆ, 1990; COLUCCI & PUCILLO, 2010) (anecdotally, three in a row), chimney circulation is disturbed in the Modrič Cave and surface air is pushed into the caves through the fractured bedrock due to the pronounced barometric high. Similar reversed airflow is recorded in the Postojna Cave during the strong NE wind with gusts of >10 m/s (KUKULJAN et al., 2021). If airflow is not mea- sured, such events can be distinguished by sudden decreases of cave air relative humidity, as recorded in March 2013 in Manita peć and two other adjacent caves (SURIĆ et al., 2017). An im- mediate lowering of CDC can be revealed by continuous daily measurement as it was conducted e.g. in Bunker Cave during the strong southern winds (RIECHELMANN et al., 2019), while our monthly measurement registered only the slight decrease of CDC after the onset of the warm season increase (5/2017, 4/2018, 5/2019, 3/2020) (Tab. A1). Impact of the south-eastern scirocco wind was not perceived, but probably might be instrumentally measured, similar to the Postojna Cave where the southern wind increases the winter updraft (KUKULJAN et al., 2021). In fact, these reversal and/or amplifying effects can occur in all seasons, but the predominant chimney effect can be overridden only by the strongest wind gusts (KUKULJAN et al., 2021). This second- ary wind-induced ventilation may have ramifications for speleo- them record interpretation when it comes to dry and windy gla- cial periods in which summer high CDC could have been suppressed, enabling speleothem precipitation. An opposite effect, i.e. an increase of CDC, may be related to intense precipitation that increases groundwater infiltration in the cave, which in turn elevates the CO2 concentration through degassing from the drip water (HOUILLON et al., 2017; BOURGES et al., 2020). Although two extreme rain events oc- curred during the monitoring period (daily precipitation of 229 mm on 11 Sept 2017 and 151 mm on 5 Jun 2020), increased CDC values were not observed during the monthly visit. This implies that short-term rain (and infiltration) events do not affect CDC on a monthly scale in terms of consequent growth cessation, par- ticularly when site-specific settings of the aquifers are consid- ered. Stalagmate® drip logger data point to a wide range of flow regimes (BAKER et al., 1997), from an immediate response due to fracture flow in the Manita peć Cave (SURIĆ et al., 2017) to practically unresponsive homogenised drip rates in the right pas- sage of the Modrič Cave (SURIĆ et al., 2018). 5.4. Influence of visitors on cave CDC and/or the opposite impacts Any human presence in the caves can elevate air temperature, relative humidity and dust content in the air, as well as disturb its chemical composition which can all potentially threaten speleo- them formation. Upon cessation of the use of open fire and acet- ylene lighting in show caves (in Modrič Cave it was part of an adventure offer until 2015), breathing remains the only direct hu- man influence on the cave air chemical composition. In exhaled human breath, CO2 concentration is ~20,000-58,000 ppm (BY- RNES et al., 1997), and in specific circumstances in the caves, it appears to serve as a high-concentration source of CO2 (PRELOVŠEK et al., 2018). Individual production, i.e. CO2 ex- halation rate, depends on a person’s age and physical activity. Some estimated and calculated values are: 0.2-1.2 LCO2 min-1 per- son-1 (DRAGOVICH & GROSE 1990), 0.39 ± 0.11 LCO2 min-1 person-1 (FAIMON et al., 2006) and 0.35-0.45 LCO2 min-1 person-1 (MILANOLO & GABROVŠEK, 2009). The contribution of CO2 from human breathing (ΔCCO2) can be calculated by the expres- sion (1) (PRELOVŠEK et al., 2018): ΔCCO2 = JA × t × nv / Vest (1) where ΔCCO2 is change of CDC due to the exhalation (in ‰), JA is CO2 production (exhalation) rate (in LCO2 min-1 person-1), t is the residence time of the visitor (in minutes), nv is number of visi- tors, and Vest is estimated volume of the cave/passage (in m3). In the Manita peć Cave, with its relatively short working hours, in August there are only ~130 visitors per day (2020 not taken in account due to COVID-19 pandemic), and with their ave- rage residence time of 30 minutes in the total cave volume of 67,510 m3, they contribute to the overall CDC with 12-26 ppm per day. Seasonal peak attendance in the Modrič Cave is 30 visi- tors per day and their trip takes place in the left passage, roughly estimated at 10,000-13,000 m3 of total volume. During the 2-hour tour, their contribution to the natural CDC is approximated to 55-162 ppm, which is six times higher than in Manita peć Cave. Both of these estimations are calculated with a theoretical absence of ventilation. A similar increase of 5.6 to 28 ppm per adult- equiva lent person per hour was measured in the Grotta di Ernesto (FRISIA et al., 2011). Our calculated values corroborate the measurements given in Tab. 1 and reflect prudent management of both caves in the sense of environmental protection. An opposite effect, i.e. the impact of high cave air CDC on visitors, can be expected in summer since the high tourist seasons coincides with the period of the elevated naturally occurring CO2 (Figs. 2a, 3 and 5b). In the Manita peć Cave, the highest recorded CDC value of 1415 ppm has no influence on visitors, as that is around the level commonly reached indoors, but values that oc- cur along the Modrič Cave tourist path are already 20-25 times higher than those of the outside atmosphere. Luckily, CDC peaks are reached only in September, after the tourists’ peak in August. Potentially harmful CDCs >10,000 ppm that can cause increased respiratory rate, respiratory acidosis, metabolic stress, increased brain blood flow and increased minute ventilation (AZUMA et al., 2018) have been recorded in the right passage which is only of scientific interest and not visited by tourists. However, there is an additional health risk in that part of the cave. It relates to the radioactive gas radon which is emitted from the deeper Earth’s crust without any surface input. According to preliminary obser- vation (SRŠEN, 2019), given its good correlation with CDC, and dependence of its concentration exclusively on dilution with sur- face air, we may expect potentially dangerous values during the summer season in the right passage. 5.5. Potential impact of long term natural and anthropogenic environmental changes to the surface on speleothem-based palaeoclimate interpretation Contemporary vegetation cover that consists of scrubby Mediter- ranean maquis-like plants has been subject to permanent natural, and more recent human-induced, changes that result in pro- or degradation of the soil horizon and plant density – the main source of CO2 in our studied sites. On decadal to centennial scales, the earliest anthropogenic impact manifested by enhanced erosion due to deforestation can be detected in marine sediment from Modrič Bay back to 1715 cal BP, with maximum at 160-265 BP (HASAN, 2017). Velebit woodlands across the wider region experienced drastic changes, as they were overused during the 16th-17th c. not only by the Venetians, Habsburgs and Otomans (ŠTEFANEC, 2000), but also by the growing local population G eo lo gi a C ro at ic a 282 Geologia Croatica 74/3 (RUKAVINA, 1990). This also coincided with the Little Ice Age with increased demands for firewood (KUŽIĆ, 1999). Under the French government starting at 1805, and with ameliorated climate conditions, erosion and/or deforestation declined (HASAN, 2017). Organized reforestation began in the late 19th century (KASER, 1987) and was intensified during the ban on goat breed- ing in 1954-1982, but the recovery has been relatively slow. Evi- dent changes of vegetation cover on the decadal scale have been documented by aerial photography (Fig. 11). Bare karst scenery that dominated in 1959 and 1973 was partially changed by planned reforestation (recorded in 1989), followed by natural (and occasional anthropogenic) forestation during the last three de- cades. Each of these soil or/and vegetation alterations might have left an imprint in CO2-controlled speleothems growth rate. Going farther back into the past, beyond human interference, climate changes at the centennial to millennial scale controlled environmental settings in terms of temperature and/or humidity variations and hence cave ventilation, which, in turn, forced or ceased speleothem precipitation. Throughout the glacial periods, commonly regarded as cold, dry and windy, in ice-covered and some periglacial regions, speleothem deposition completely ceased (BAKER et al., 1995; LOWE & WALKER, 1998). This was due to the lack or negligible input of pedogenic CO2 into the karst system because of the absence of a soil cover (SPÖTL et al., 2006; LI et al., 2021). However, that was not the case in littoral Croatia, as evidenced in currently submerged speleothems that precipitated during the Last Glacial Maximum (SURIĆ & JURAČIĆ, 2010), and particularly in speleothems from the Manita peć Cave where sufficient pedogenic CO2 sustained karst processes, including speleothem deposition, throughout the last glacial cycle (SURIĆ et al., 2021). Presumably, the possibility of growth cessation caused by a diminished gradient between pCO2 Figure 11. Natural and anthropogenic environmental transformations on the surface above the Modrič Cave between 1959 and 2020. Modrič Cave plan is given in red. G eologia C roatica 283Surić et al.: Spatio-temporal variations of cave-air CO2 concentrations in two Croatian show caves: natural vs. anthropogenic controls in drip water and cave air was compensated by enhanced wind activity (WACHA et al., 2013; DURN et al., 2018; KOVAČIĆ et al., 2013) which promotes cave ventilation (RIECHELMANN et al., 2019). As for the past interglacials, likewise today, growth interruptions due to enhanced biological activity, elevated CDCs and hindered degassing have been possible in the Modrič Cave. Given that the potential growth cessation occurs only seasonally, the winter signal may dominate in other speleothem climate-re- lated properties and proxies driven by CO2-flux, as well (GENTY et al., 2001; BALDINI et al., 2008; FRISIA et al., 2011). One such commonly used proxy is δ13C, which increases with vegetation decline related to climate deterioration, accompanied finally by the cessation of speleothem growth (FRISIA et al., 2011). In ad- dition, cave ventilation forces degassing of CO2 from dripwater, prior to any calcite precipitation onto the stalagmites (FRISIA et al., 2011). Prior calcite precipitation leads to 13C-enrichment in the speleothems (FAIRCHILD & BAKER, 2012) during deposi- tion within the cave atmosphere obviously favourable for their growth. These similar signals, but supported by opposite condi- tions, underscore the importance of a multiproxy approach to verify palaeoclimate interpretations. 6. CONCLUSIONS We presented the results of multiyear monitoring of CDC in the Modrič and Manita peć show caves, which was conducted in or- der to identify spatio-temporal CDC variations, their controlling mechanisms and potential mutual influence and interrelation- ships between cave atmosphere and visitors. i) The main sources of CO2 in both caves are plant- and mi- crobial-derived CO2 produced in the soil horizon by root respira- tion and decay of organic matter that is transported downward, and in-cave CO2 degassing of the dripping groundwater. Under- ground streams are absent and CO2 production by cave biota is considered negligible. The main sink for the cave air CO2 is dilu- tion with outside air due to the cave ventilation which is governed by air density differences derived from different air temperature, and by occasional wind-induced air flow. ii) General ventilation patterns are seasonal and mimic the chimney-type circulation with associated CDC variations: the winter mode includes inflow of cold, dense CO2-poor outside air into the caves due to the Tout < Tcave, while in summer mode, warm surface CO2-rich air enters into the caves during Tout > Tcave. The key events are abrupt transitions from Tout > Tcave to Tout < Tcave followed by a sudden CDC drop. Occasionally, NE bora wind-induced air flow, as a secondary ventilation pattern, overprints the primary ventilation model, while the influence of wind-driven ventilation of the SE scirocco was not noticed. iii) Superimposed upon the ventilation driven by air density gradient are circulation effects controlled by cave geomorpho logy and epikarst architecture, so the similar seasonal ventilation patterns result in large differences between absolute CDC values in the inclined and spacious Manita peć Cave, and the horizontal and more confined Modrič Cave. Moreover, within the same cave, the right and left Modrič Cave passages are ventilated differently due to the fractured fault zone of passable left passage (more ven- tilated) and more constrained right one (less ventilated). iv) Although these caves are only 8 km apart, belong to the same type of climate (Cfa) and vegetation zone (Mediterranean), and spatio-temporal CDC variations within them are generally controlled by the same dynamic (seasonal) ventilation patterns, the magnitude of CDC variation appears to be site-specific. Due to the dependence of calcite precipitation on CDC variation, care- ful selection of the samples for speleothem-based palaeoenviron- mental studies is essential. In particular, the Manita peć Cave generally does not experience major CO2 fluctuations, so neither deterioration by condensation corrosion of the already deposited calcite, nor growth inhibition due to the CDC fluctuations is ex- pected. On the other hand, the very high summer-autumn CO2 concentration within Modrič Cave could reduce CO2 degassing from the dripwater and thus hamper calcite precipitation. v) Due to the low number of visitors, anthropogenic impacts on cave CDC is negligible even in the confined Modrič Cave pas- sages, when compared to the natural CO2 input which is higher by two orders of magnitude. In the Manita peć Cave episodes with slightly elevated human-induced concentrations are occa- sional and temporary short-duration events, with insignificant contribution to the natural CO2 content. vi) Conversely, given the site-specific nature of CDC and known temporal patterns, cave management should maintain the same practice of short visits of small groups in Manita peć Cave and the left passage of Modrič cave, while the right one should be avoided at least in late summer and during autumn. vii) Elevated CDC values and similar preliminary results of radon measurements urge high-resolution (daily to hourly) moni- toring of both parameters, measurement of velocity and the di- rection of air flow, along with collection of modern calcite to as- sess its precipitation in relation to the ventilation dynamics. ACKNOWLEDGEMENT We are grateful to the Public Institution Natura Jadera and Pa- klenica National Park executives and staff for their kind coope- ration and support. 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April 2020 data are missing due to the COVID-19 pandemic lockdown. For the measurement points, reader is referred to the Fig. 7. Main passage Left passage Right passage M00 M11 M22 T13 T14 T15 M31 M32 3 Mar 2017 385 490 441 994 1475 4 Apr 2017 385 427 528 1107 1580 2 May 2017 393 412 458 1067 1666 2 Jun 2017 393 2115 2244 2536 2558 4 Jul 2017 380 3600 4450 4850 4900 31 Jul 2017 5155 5110 6517 6600 5 Sep 2017 386 4800 4900 7070 7620 3 Oct 2017 373 415 2813 5138 6145 31 Oct 2017 383 388 1358 4180 4892 5 Dec 2017 387 382 411 2060 3522 4 Jan 2018 366 378 416 1028 1858 30 Jan 208 438 454 485 1161 1769 1 Mar 2018 459 606 504 1640 2153 6 Apr 2018 418 492 545 1230 1915 1 May 2018 534 1886 1940 2278 2434 1 Jun 2018 475 3081 3247 3879 3903 5 Jul 2018 466 4772 4812 4713 4645 4752 7058 7228 1 Aug 2018 487 5605 5620 5459 5432 5576 8810 8805 7 Sep 2018 498 5723 6273 5781 5738 5871 8874 9386 2 Oct 2018 388 5286 6485 8441 7831 6955 8215 9213 2 Nov 2018 350 4252 4635 5200 5310 5293 4995 5812 4 Dec 2018 458 614 521 554 551 1252 3095 4404 4 Jan 2019 425 462 496 529 504 572 1657 2247 31 Jan 2019 433 548 506 480 493 559 1447 2251 5 Mar 2019 434 463 491 501 498 580 1245 1880 2 Apr 2019 436 481 647 702 754 829 1820 2317 2 May 2019 440 461 525 540 544 640 1269 1940 31 May 2019 444 1170 1548 1808 2036 2098 2505 2613 2 Jul 2019 520 3817 3846 3818 3849 3889 6195 6250 1 Aug 2019 590 5313 5276 5214 5149 5211 8263 8550 3 Sep 2019 422 6565 6868 6556 6533 7228 >10000>10000 1 Oct 2019 482 6702 6731 6709 6636 6680 9614 >10000 5 Nov 2019 564 3877 4220 5377 5752 5789 5314 6310 3 Dec 2019 418 510 627 715 711 944 3104 4015 3 Jan 2020 454 480 509 533 525 610 1358 2226 6 Feb 2020 455 465 506 517 497 612 1617 2200 3 Mar 2020 427 456 554 500 504 551 1293 1795 1 Apr 2020 5 May 2020 439 513 705 759 900 1174 1590 2149 5 Jun 2020 513 2755 2845 3030 3095 3150 3689 3924 30 Jun 2020 584 4242 4234 4224 4212 4206 5420 5473 3 Aug 2020 473 5495 5635 5317 5300 5481 8750 8867 1 Sep 2020 477 2700 6070 6015 5960 6028 9790 >10000 1 Oct 2020 574 1128 1680 2730 3100 3190 4670 6763 3 Nov 2020 468 500 592 636 665 930 2976 4005 4 Dec 2020 440 475 571 562 560 649 1698 3052 8 Jan 2021 441 525 504 518 512 584 1425 2197 1 Feb 2021 448 467 517 505 512 580 1243 1783 3 Mar 2021 476 491 537 557 548 601 1419 2064 Table A2. Manita peć Cave air CO2 concentration (in ppm) measured during the 2018-2021 period. April 2020 data are missing due to the COVID-19 pandemic lockdown. For the measurement points, reader is referred to the Fig. 8. MP 01 MP 02 MP 03 MP 04 MP 05 MP 06 MP 07 MP 08 MP 09 4 Jan 2018 325 339 325 351 348 400 397 398 421 30 Jan 2018 414 411 404 441 444 407 464 414 413 1 Mar 2018 354 373 412 411 422 412 413 415 415 6 Apr 2018 391 387 400 414 415 422 414 415 441 1 May 2018 378 380 452 524 505 512 510 502 551 1 Jun 2018 463 535 693 814 825 812 816 821 845 5 Jul 2018 422 497 684 855 900 903 920 911 924 1 Aug 2018 430 599 740 1243 1270 1259 1315 1346 1387 7 Sep 2018 426 501 563 1166 1173 1170 1212 1198 1226 2 Oct 2018 397 612 824 851 753 655 745 650 2 Nov 2018 382 400 432 585 588 578 586 595 604 4 Dec 2018 380 400 418 457 411 419 428 412 416 4 Jan 2019 377 381 394 401 424 421 412 419 450 31 Jan 2019 411 405 395 407 405 406 402 409 417 5 Mar 2019 395 402 404 412 418 414 415 418 435 2 Apr 2019 402 401 407 428 426 429 431 427 429 2 May 2019 413 407 411 435 465 469 471 466 476 31 May 2019 383 409 430 515 527 523 525 523 538 2 Jul 2019 404 406 657 897 914 917 946 933 925 1 Aug 2019 389 493 884 1185 1196 1179 1186 1210 1237 3 Sep 2019 379 399 423 1048 1335 1323 1338 1415 1410 1 Oct 2019 402 465 600 923 979 978 979 990 988 5 Nov 2019 418 664 410 722 747 747 747 767 770 3 Dec 2019 402 414 407 414 407 402 424 415 472 3 Jan 2020 422 439 426 425 428 435 427 427 418 6 Feb 2020 413 416 435 445 420 421 408 407 460 3 Mar 2020 401 417 408 410 424 422 418 426 424 1 Apr 2020 5 May 2020 405 405 419 428 409 420 428 435 442 6 Jun 2020 448 422 437 488 513 514 505 519 30 Jun 2020 392 435 616 738 738 762 758 746 778 3 Aug 2020 397 422 718 1054 1076 1072 1127 1137 1152 1 Sep 2020 394 424 576 1164 1140 1137 1142 1198 1210 1 Oct 2020 415 436 458 696 706 712 719 734 740 3 Nov 2020 434 428 436 500 533 530 535 539 554 4 Dec 2020 416 407 435 434 431 420 413 416 438 8 Jan 2021 397 416 425 434 434 433 434 428 433 1 Feb 2021 432 441 405 424 431 431 430 435 463 3 Mar 2021 420 427 450 444 446 448 448 447 458 APPENDIX