Intermediate water ventilation in the Nordic seas during MIS 2

Abstract

[1] A high-resolution marine record from the northern Norwegian continental margin off Lofoten is used to reconstruct changes in the oceanography of the Nordic seas during marine isotope stage (MIS) 2 including the Last Glacial Maximum and early deglaciation circa 25 to 16 ka. The period was characterized by generally warm subsurface water temperatures >2 C and inflow of Atlantic surface water. Several events were characterized by decrease in ventilation of the intermediate water and low subsurface temperature and salinity. They correlate with colder atmospheric temperatures as seen in ice cores. The events terminated with gradual strengthening of the intermediate water ventilation and increase in subsurface temperature. The generation of intermediate water was unstable and experienced climate and ventilation changes on millennial and centennial timescales. The changes appear consistent with modeling experiments that predict short-lasting circulation stops during MIS 2 due to release of meltwater in the Nordic seas.

Nordic Seas polynyas and their role in preconditioning marine productivity during the Last Glacial Maximum

“…The open marine biomarker dinosterol mainly follows the variability in the IP 25 record during the LGM (Fig. 5 ), while the number of planktic foraminifera is also highest during the LGM, consistent with the widely observed elevated biogenic calcite content in LGM sediments along the entire Barents Sea continental margin 21 , 39 – 41 . Both IP 25 concentration and planktic foraminifera drop to minimal values during the initial deglaciation (Fig.…”

“…6 ) 44 and reduced phyto- and zooplankton productivity indicators 41 . In the SW Barents Sea, decreased ventilation of Atlantic intermediate waters and progressive surface cooling in the study area 39 between 18.3 and 17.7 ka BP may have increased the sea ice concentration, as indicated by a gradual decline in IP 25 (Fig. 6 ).…”

“…The positioning of moderately abundant IP 25 concentrations in pre-LGM deposits indicate the presence of the polar front at the study area and, therefore, subduction of Atlantic water-derived water masses below seasonally sea ice covered surface waters. The accompanying high abundance of calcareous organisms 21 , 39 would have resulted from the prevalence of sub-surface Atlantic water masses penetrating the eastern Nordic Seas below seasonal to perennial sea ice cover 14 , 43 . In contrast, further north, and towards the Fram Strait, sea ice cover was more permanent and primary productivity significantly reduced between 28 and 26 ka BP 44 .…”

High-resolution record of late glacial and deglacial sea ice changes in Fram Strait corroborates ice–ocean interactions during abrupt climate shifts

“…A significant though highly variable Atlantic water inflow to the southern part of the GIN Seas, however, is also suggested by e.g. Rasmussen and Thomsen (2008), Rørvik et al (2013) and Weinelt et al (2003) from foraminifer data. A model simulation by Stärz et al (2012) using GLAMAP SST data (see Fig.…”

Dynamic intermediate ocean circulation in the North Atlantic during Heinrich Stadial 1: A radiocarbon and neodymium isotope perspective

“…Deep storage and decay of radiocarbon could also have occurred in that silled basin before the water overflowed to become incorporated into the mid‐depth Atlantic basin. Intermediate water formation in the Norwegian Sea was highly variable towards the end of the last glacial period, with millennial and centennial changes in ventilation [ Rorvik et al , ], indicating also the potential for changes over short timescales as required by the deep‐sea coral data. Deep water formation by brine rejection has also been invoked to explain anomalously light oxygen and carbon isotopes in the Norwegian Seas during Heinrich Stadial 1 [ Dokken and Jansen , ] and such a water mass may have been exported into the intermediate to mid‐depth North Atlantic [ Meland et al , ; Waelbroeck et al , ], providing a radiocarbon‐depleted source to both the northeast Atlantic [ Thornalley et al , ] and the New England Seamounts.…”