Diatom responses to Holocene environmental changes in a karstic Lake Vrana in Dalmatia (Croatia)

Stable Isotope Hydrology of Cave Groundwater and Its Relevance for Speleothem-Based Paleoenvironmental Reconstruction in Croatia

“…The relationship between rain and drip water δ 2 H-δ 18 O pairs of coastal and insular sites is shown in Figure 5. MOD, MP and SP caves are presented by at least one-year series of rain and drip water monthly-integrated samples and associated LMWLs, while MED, VRD, KRA, VML and MML are represented by data from one-two drip water samples.…”

“…The relationship between precipitation and drip water isotopic composition of continental sites NG, LOK, GB, DB and DC is given in Figure 6. δ 2 H and δ 18 O have wide ranges due to the strong seasonal temperature variations [68], among which DC's smallest amplitude (Table 2) reflects its southernmost position (Figure 1). Drip water isotopic values of NG, GB and DB sites suggest larger contributions of winter precipitation, with a difference between amount-weighted annual mean precipitation and average drip water δ 18 O of 0.7% in NG cave, 0.8-1.2% in GB and 1.1-1.2% in DB cave (Table 3), at least for the monitoring period [36].…”

“…Caves with lower temperatures (LOK and DC) showed a different pattern; their drip water mean δ 18 O values were distributed around the amount-weighted annual mean of precipitation δ 18 O (Table 3), with indistinguishable preferential recharge period Figure 6. δ 2 H-δ 18 O relationship of monthly integrated drip water (crosses) and rainwater samples (dots) with associated local meteoric waterlines in mid-altitude continental caves NG, LOK, DB, GB, DC.…”

“…According to the drip water samples from VEL cave, these aquifers are predominantly fed by September-May precipitation [39]. Average annual duration of snow cover (≥ 1 cm) in that region is 165 days (Zavižan station 1981-2010, CMHS, 2020) and most of the recharge is meltwater, hence the grouping of drip water δ 2 H-δ 18 O data along the lowermost part of the NV MWL (Figure 7). The difference between the amount-weighted annual mean precipitation and average drip water δ 18 O is 0.1-0.2% (Table 3, Figure 8), although Figure 7 would suggest a larger difference.…”

“…Other studied Croatian regions would fit into the class with MAAT between 10 °C and 16 °C (we included here also MOD region with MAAT 16.6 °C, as a marginal case) in which the drip water δ 18 O may be affected by evaporative fractionation of the water in the soil and epikarst or by selective recharge, resulting in |Δδ 18 Oprec-drip|> 0.3‰ [77]. Such values are recorded in MOD, NG, DB and GB caves, but not in the two littoral caves, MP and SP, which are characterized with |Δδ 18 Oprec-drip|< 0.3‰, as if they were 'cold' caves.…”