Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean

Abstract

Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean. Boreas, Vol. 30, pp. 2-16. Oslo. ISSN 0300-9483.Foraminiferal assemblage s were studied in northern Barents Sea core ASV 880 along with oxygen and carbon isotope measurement s in planktoni c (N. pachyderm a sin.) and benthic (E. clavatum ) species. AMS C-14 measurements performed on molluscs Yoldiella spp. show that this core provides a detailed and undisturbe d record of Holocene climatic changes over the last 10 000 calendar years. Surface and deep waters were very cold (< 0°C) at the beginning of the Holocene. C. reniforme dominated the highly diverse benthic foraminiferal assemblage . From 10 to 7.8 cal. ka BP, a warming trend culminated in a temperature optimum, which developed between 7.8 and 6.8 cal. ka BP. During this optimum, the input of Atlantic water to the Barents Sea reached its maximum. The Atlantic water mass invaded the whole Franz Victoria Trough and was present from subsurface to the bottom. No bottom water, which would form through rejection of brine during winter, was present at the core depth (388 m). The water strati cation was therefore greatly reduced as compared to the present. An increase in percentag e of I. helenae/norcrossi points to long seasonal ice-free conditions. The temperature optimum ended rather abruptly, with the return of cold polar waters into the trough within a few centuries . This was accompanie d by a dramatic reductio n of the abundanc e of C. reniforme. During the upper Holocene, the more opportunisti c species E. clavatum became progressivel y dominant and the water column was more strati ed. Deep water in Franz Victoria Trough containe d a signi cant amount of cold Barents Sea bottom water as it does today, while subsurface water warmed progressivel y until about 3.7 cal. ka BP and reached temperatures similar to those of today. These long-term climatic changes were cut by several cold events of short duration, in particula r one in the middle of the temperatur e optimum and another, which coincides most probably with the 8.2 ka BP cold event. Both long-and short-ter m climatic changes in the Barents Sea are associate d with changes in the ow of Atlantic waters and the oceanic conveyor belt. Jean-Claud e Duplessy

Holocene climate in the subarctic fjord Malangen, northern Norway: a multi‐proxy study

“…The U. mediterranea record from the northern North Sea (Fig. 9A) , the benthic 18 O record from the eastern Barents Sea (Duplessy et al 2001) (Fig. 9E) as well as the Malangen temperature curve (Fig.…”

“…However, the mid and late Holocene cooling is not reflected by increased 18 O in these records. A possible explanation is that mid and late Holocene cooling in the eastern Barents Sea was characterized by increased influence of cool, low saline and 18 O-depleted Arctic Water (Hald et al 1999;Duplessy et al 2001;Lubinski et al 2001).…”

Centennial‐to‐millennial‐scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75°N

“…comm. 2001 on sediment record MD95-2011), likewise subsurface penetrations of Atlantic water into the Arctic Ocean (Duplessy et al 2001;Hald et al 1999;Lubinski et al 1996Lubinski et al , 2001. The isotopic and chemical signatures in the Greenland ice and at the Greenland margin show analogous fluctuations over the Holocene, although at much lower amplitudes (Willemse & Tørnquist 1999;Mayewski et al 1997;Grootes & Stuiver 1997;Schulz & Paul 2002).…”

The Global Thermohaline Paleocirculation

“…Although the oxygen isotope composition of planktic foraminifera mainly displays the global ice volume and ambient water temperature (e.g., Emiliani 1955;Shackleton 1974), it was ascertained already in the 1960s that the δ 18 O values also correlate with sea-surface salinity changes (e.g., Craig and Gordon 1965;Ivanova et al 1985;Duplessy et al 1991bDuplessy et al , 1992, since both parameters depend on the hydrological cycle (precipitation + runoff -evaporation). In the Arctic, variations in planktic and benthic oxygen isotope ratio during the last glaciation also monitor the Atlantic water input (e.g., Duplessy et al 2001Risebrobakken et al submitted, see Chapter 4) whereas in the North Atlantic they enable to trace the freshwater discharge in the surface water layer and the transfer of this signal to the intermediate depth during the brines rejection (see Chapter 3 and Chapter 4). Thus, in fact the oxygen and carbon isotope data provide the valuable tools to reconstruct the shifts in location and depth of the deep convection during the abrupt climate changes (Vidal et al , 1998Dokken and Jansen 1999;see Chapter 3).…”

“…The temperature change by 0.24 • C was considered corresponding to 1‰ change in local oxygen isotope value of sea water (Shackleton 1974;Duplessy et al 2001;Section 4.5.4). These variations were derived from planktic and benthic oxygen isotope measurements removing the global ice volume.…”