Past climate variations recorded in needle-like aragonites correlate with organic carbon burial efficiency as revealed by lake sediments in Croatia

Abstract

The drivers of organic carbon (OC) burial efficiency are still poorly understood despite their key role in reliable projections of future climate trends. Here, we provide insights on this issue by presenting a paleoclimate time series of sediments, including the OC contents, from Lake Veliko jezero, Croatia. The Sr/Ca ratios of the bulk sediment are mainly derived from the strontium (Sr) and calcium (Ca) concentrations of needle-like aragonite in Core M1-A and used as paleotemperature and paleohydrology indicators. Four major and six minor cold and dry events were detected in the interval from 8.3 to 2.6 calibrated kilo anno before present (cal ka BP). The combined assessment of Sr/Ca ratios, OC content, carbon/nitrogen (C/N) ratios, stable carbon isotope (δ13C) ratios, and modeled geochemical proxies for paleoredox conditions and aeolian input revealed that cold and dry climate states promoted anoxic conditions in the lake, thereby enhancing organic matter preservation and increasing the OC burial efficiency. Our study shows that the projected future increase in temperature might play an important role in the OC burial efficiency of meromictic lakes.

A Holocene Sedimentary Record and the Impact of Sea-Level Rise in the Karst Lake Velo Blato and the Wetlands on Pag Island (Croatia)

“…Coastal lakes and wetlands host large and dynamic reservoirs of organic carbon. Higher values of TOC are evident in isolated karst basins during the freshwater phase, compared to recent marine and lake sediments [14,15,23,26,27].…”

“…In the central and eastern Mediterranean, a wetter climate prevailed in early to mid-Holocene [28][29][30][31], followed by the drier climate conditions during the mid-Holocene, and several arid phases, with considerable site-to-site differences [2,[31][32][33]. In the Adriatic Sea marine sediment core records, the wet early to mid-Holocene was determined [34,35], supported by the lake and marine sediment cores in the eastern Adriatic Sea [10,14,15,18,23,26,27,36,37]. High-resolution paleoclimate reconstruction was possible in lake sediments in the period of the deep-lake phase, between 8300 and 2600 cal yr BP, in Veliko Jezero on the Island of Mljet with four major and six minor cold and dry events identified [27], which correlates well with Adriatic marine cores [35,38].…”

“…In the Adriatic Sea marine sediment core records, the wet early to mid-Holocene was determined [34,35], supported by the lake and marine sediment cores in the eastern Adriatic Sea [10,14,15,18,23,26,27,36,37]. High-resolution paleoclimate reconstruction was possible in lake sediments in the period of the deep-lake phase, between 8300 and 2600 cal yr BP, in Veliko Jezero on the Island of Mljet with four major and six minor cold and dry events identified [27], which correlates well with Adriatic marine cores [35,38].…”

“…This is evidenced on the eastern Adriatic coast by submerged freshwater lakes and wetlands in Lake Veliko and Stupa Bay on the Island of Mljet [16,18], in Pirovac Bay [19], as well as a sub-marine archaeological Roman site and salt marsh in the Caska Bay on the Island of Pag [20,21], and prehistoric pile-dwellings in Zambratija Bay [22]. Most of the freshwater lakes on the eastern Adriatic coastal area formed during the Late Pleistocene/Early Holocene, such as Lake Vrana [23][24][25], a lake in Bokanjačko Blato [26], the Baćina Lakes (Crniševo) [19], and Lake Veliko on the Island of Mljet [16][17][18]27]. Holocene palaeohydrological changes from shallow to deeper lakes are driven by the sea level rise, while climate variability was only partly recorded, also due to the low resolution.…”

“…Holocene sea-level rise data points were determined on specific localities on the Eastern Adriatic Sea: in Lošinj Bay [14,15], in Novigrad and the Karin Sea [44,45], in Veliko Jezero and Stupa Bay on the Island of Mljet [16,27], in Caska Bay on the Island of Pag [20], in western Istria [46], in the Mirna and Neretva valleys [47], and on submerged speleothem records along the eastern Adriatic coast [48,49]. The salt pans and fish tanks were also used as sea-level markers on the eastern Adriatic coast [50][51][52], as well as archaeological and biological markers [53][54][55].…”