Reconstruction of mid- to late-Holocene winter temperatures in the Skagerrak region using benthic foraminiferal Mg/Ca and δ¹⁸O

Abstract

Reconstruction of Skagerrak deep-water renewal is used to assess regional changes in winter thermal conditions over the past 6800 years. Changes in winter climate conditions from the Skagerrak region are in turn linked to shifts in Holocene large-scale atmospheric circulation patterns prevailing over northern Europe. We use Melonis barleeanus Mg/Ca from two sediment cores in the central Skagerrak to reconstruct temperature of Skagerrak intermediate water, representing the warm season temperature variability, and deep water, for monitoring Skagerrak deep-water renewal, reflecting the winter temperature variability. In addition, M. barleeanus δ18O is used from the deeper core to reconstruct salinity, also monitoring the deep-water renewal. Our results show that the Skagerrak deep-water experienced phases of particularly enhanced renewal during the mid-Holocene reflecting severe winter conditions, followed by a general shift to reduced renewal as a consequence of milder winter conditions over the North Sea around 3500 cal. yr BP. The late-Holocene shift was most likely related to the onset of a regime with intensified winter westerly winds directed toward northern Europe and an increased inflow of North Atlantic water into the Skagerrak–North Sea reflecting more maritime climate conditions. On millennial scale, cold phases in our deep-water records match with low winter precipitation phases in western Norway. They are associated with distinct increases in ice rafted debris (IRD) in North Atlantic sediments, suggesting that phases of iceberg discharge in the Atlantic were associated with cold and dry winter conditions over northern Europe. Interestingly, the cold event centered around 5900 cal. yr BP appears to be only associated with winter variability, while the following one at 4200 cal. yr BP is documented in our winter record, as well as in records related to warmer seasons.

Reconstructing Holocene temperature and salinity variations in the western Baltic Sea region: a multi-proxy comparison from the Little Belt (IODP Expedition 347, Site M0059)

“…4). An interval of generally higher mean annual air and water temperatures has previously been described from other records of the Baltic Sea region such as Lake Flarken, Sweden (Seppä et al, 2005) or the Skagerrak (Butruille et al, 2017;Krossa et al, 2017) and is consistent with the Holocene Climate Optimum (HCO, also Holocene Thermal Maximum; e.g. Seppä et al, 2005).…”

“…Ideally, multiple proxies should therefore be used simultaneously to provide independent paleotemperature records (e.g. Butruille et al, 2017;Jonas et al, 2017).…”

Holocene environmental history of the Ångermanälven Estuary, northern Baltic Sea

“…The timing and magnitude of the temperature increase are comparable to those previously reported for the HTM from several marine (Butruille et al . ) and terrestrial palaeoenvironmental records (Seppä et al . ) of central and northern Europe.…”

Coastal primary productivity changes over the last millennium: a case study from the Skagerrak (North Sea)

“…river runoff and precipitation could lead to reduced salinity in the central Skagerrak which influence the δ 18 O and BWT signals (Ravelo and Hillaire-Marcel, 2007;Brückner and Mackensesn, 2008;Erbs-Hansen et al, 2011;Butruille et al, 2017). Thus, it is possible that the distinct differences in BWT and δ…”

“…For the stable carbon and oxygen isotopes (δ 13 C, δ 18 O) and trace elements analyses, well-preserved tests of benthic foraminifera Melonis barleeanum were picked from the dried sediment (fraction >150 μm). Melonis barleeanum was selected for the analyses due to its relatively high abundance in the whole study record at both sites and its proved potential for 25 geochemical palaeoreconstructions (Mackensen et al, 2000;Kristjánsdóttir et al, 2007;Brückner and Mackensen, 2008;Butruille et al, 2017). Stable isotopes measurements were performed at 1 cm intervals and the trace elements analyses were done at 1 -2 cm intervals from both gravity cores down to 170 cm (EMB046/20-3GC) and 164.5 cm (EMB046/10-4GC with methanol using an ultrasonic bath and dried at 60 ºC.…”