Oceanic heat advection to the Arctic in the last Millennium

EGU2011-8738 At present, the Arctic is responding faster to global warming than most other areas on earth, as indicated by rising air temperatures, melting glaciers and ice sheets and a decline of the sea ice cover. As part of the meridional overturning circulation which connects all ocean basins and influences global climate, northward flowing Atlantic Water is the major means of heat and salt advection towards the Arctic where it strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ca. 150 years. To reconstruct the history of temperature variations in the Fram Strait Branch of the Atlantic Current we analyzed a marine sediment core from the western Svalbard margin. In multidecadal resolution the Atlantic Water temperature record derived from planktic foraminifer associations and Mg/Ca measurements shows variations corresponding to the well-known climatic periods of the last millennium (Medieval Climate Anomaly, Little Ice Age, Modern/Industrial Period). We find that prior to the beginning of atmospheric CO2 rise at ca. 1850 A.D. average summer temperatures in the uppermost Atlantic Water entering the Arctic Ocean were in the range of 3-4.5°C. Within the 20th century, however, temperatures rose by ca. 2°C and eventually reached the modern level of ca. 6°C. Such values are unprecedented in the 1000 years before and are presumably linked to the Arctic Amplification of global warming. Taking into account the ongoing rise of global temperatures, further warming of inflowing Atlantic Water is expected to have a profound influence on sea ice and air temperatures in the Arctic

The Power of VPL: Validation of Prior Learning as a Multi-targeted Approach For Access to Learning Opportunities For All

Preface from Ruud Duvekot: Learning is more than ever important and valuable, people are encouraged to invest in their potential throughout their lives, taking into account their prior learning. According to policy papers all across the globe, this should concern all citizens, including the underrepresented groups and non-traditional learners with regard to higher education because everywhere the knowledge-economy needs more higher-educated participation from all..

Mg/Ca paleotemperature reconstruction of Atlantic Water advected to the European subarctic and arctic margins in the past 14.000 cal yr B.P.

Foraminiferal Mg/Ca-ratios have proven to be valuable proxies for reconstructing past water temperatures and salinities especially in subtropical to tropical regions. However, recent studies have expanded the temperature range of the proxy to include subarctic and arctic environments. In this study we aim to reconstruct the temperatures of the inflowing Atlantic Water mass on the European arctic and subarctic margins from late glacial to the present using Mg/Ca-ratios measured on planktic and benthic foraminiferal tests. The Atlantic Water is carried towards the Arctic by the North Atlantic Current and its meriodinal extension the West Spitsbergen Current. Both currents are important components of the meridional overturning circulation system of the North Atlantic. Furthermore, these currents contribute to the relatively milder climate along their paths. The subarctic paleorecord is based on two adjacent cores from ca. 500 m water depth in the Andfjorden, North Norway covering an Allerød - present sequence constrained by 15 AMS datings. SiZer analysis indicates variable chilled bottom water temperatures during Allerød and Younger Dryas, before a significant multistep temperature increase mark the onset of the Holocene. Stable relatively high temperatures prevail throughout the Holocene with a significant but modest decline at around 3.500 cal yr B.P. The arctic paleorecord is based a core from ca. 1500 m water depth on the West Spitsbergen slope. The core covers an Allerød - present sequence constrained by 13 AMS datings. SiZer analysis indicates no significant sea surface temperatures (SSTs) during the Late Glacial/Holocene boundary presumably linked to prevailing severe sea ice conditions and melt water influence in the area. Significant SST decline is observed from the early Holocene to ca. 6.000 cal yr B.P. SST remain remains low and stable until ca. 3000 cal yr B.P. after which a significant temperature increase initiates and continues toward the present

A Late Glacial–Early Holocene multiproxy record from the eastern Fram Strait, Polar North Atlantic

The paleoceanographic development of the eastern Fram Strait during the transition from the cold Late Glacial and into the warm Early Holocene was elucidated via a multiproxy study of a marine sediment record retrieved at the western Svalbard slope. The multiproxy study includes analyses of planktic foraminiferal fauna, bulk sediment grain size and CaCO3 content in addition to Mg/Ca ratios and stable isotopes (delta C-13 and delta O-18) measured on the planktic foraminifer Neogloboquadrina pachyderma. Furthermore paleosubsurface water temperatures were reconstructed via Mg/Ca ratios (sSST(Mg/Ca)) and transfer functions (sSST(Transfer)) enabling comparison between the two proxies within a single record. The age model was constrained by four accelerator mass spectrometry (AMS) C-14 dates. From 14,000 to 10,300 cal yr B.P. N. pachyderma dominated the planktic fauna and cold polar sea surface conditions existed. The period was characterized by extensive sea ice cover, iceberg transport and low subsea surface temperatures (sSST(Transfer) similar to 2.1 degrees C; sSST(Mg/Ca) similar to 3.5 degrees C) resulting in restricted primary production. Atlantic Water inflow was reduced compared to the present-day and likely existed as a subsurface current. At ca. 10,300 cal yr B.P. Atlantic Water inflow increased and the Arctic Front retreated north-westward resulting in increased primary productivity, higher foraminiferal fluxes and a reduction in sea ice cover and iceberg transport. The fauna rapidly became dominated by the subpolar planktic foraminifer Turborotalita quinqueloba and summer sSST(Transfer) increased by similar to 3.5 degrees C. Concurrently, the sSST(Mg/Ca) recorded by N. pachyderma rose only similar to 0.5 degrees C. From ca. 10,300 to 8600 cal yr B.F. the average sSST(Mg/Ca) and sSST(Transfer) were similar to 4.0 degrees C and similar to 55 degrees C, respectively. The relatively modest change in sSST(Mg/Ca) compared to sSST(Transfer) can probably be tied to a change of the main habitat depth and/or shift in the calcification season for N. pachyderma during this period

Holocene Variability of Bottom Water Temperatures on the Western Svalbard Margin, Arctic Gateway – First Results and Open Questions

During the past decades Mg/Ca ratios have been increasingly used in order to calculate past temperature variations independent from faunal assemblages. Especially in the Fram Strait, the main pathway of heat flux to the Arctic, new temperature estimation tools are urgently needed to better understand past complex interaction of different water masses and the extent of Atlantic Water advection to the Arctic Ocean. The Holocene section of a sediment core from the western Svalbard margin has been studied at high-resolution for benthic proxy indicators to reconstruct deepwater sources and mixing in the Arctic Gateway since the last ca 10,000 years. Benthic stable isotope values and sortable silt mean grain size data are compared to a first, preliminary data set of Mg/Ca paleotemperatures established from the benthic foraminifer species Cibicidoides wuellerstorfi in the eastern Fram Strait. When compared to planktic proxy indicators, this reconstruction of past bottom water temperatures at a northernmost site allows to estimate the linkage between deepwater inflow and AW advection within the West Spitsbergen Current. Furthermore, benthic Mg/Ca temperatures can help unravelling the local impact (e.g., by brine-enriched waters) from general trends in bottom water circulation. Short-lived decreases in benthic carbon isotope values seem to correlate to cold surface water events in the area such as the 8.2 ka event. Similarly, decreases in benthic carbon isotope values in the Nordic Seas around 8 ka have been assigned to decreased bottom water ventilation possibly due to an entrainment of relatively fresh water into the thermohaline system (Bauch et al., 2001). While sluggish bottom current speeds have been found for the 8.2 ka event north of our site on the Yermak Plateau (Hass, 2002), during colder events on the Western Svalbard margin sediment data seem to anticorrelate to benthic carbon isotope data either suggesting a rather unexpected increase in bottom current velocity or an impact of brine-enriched winter waters from the fjord/trough system which might have generated increased lateral coarser-grained sediment injections (Sarnthein et al., 2003). A Late Holocene trend towards significantly higher benthic oxygen isotopes may be either related to a cooling or increasing salinity in bottom waters. Higher salinity of bottom waters may be again caused by dense water formation during winter sea-ice formation in southern and western Svalbard fjords (e.g., Quadfasel et al., 1988; Rudels et al., 2005). Bauch, H. A., H. Erlenkeuser, R. F. Spielhagen, U. Struck, J. Matthiessen, J. Thiede, and J. Heinemeier (2001a), A multiproxy reconstruction of the evolution of deep and surface waters in the subarctic Nordic seas over the last 30,000 yr, Quaternary Science Reviews, 20(4), 659-678. Hass, H. C. (2002), A method to reduce the influence of ice-rafted debris on a grain size record from northern Fram Strait, Polar Research, 21(2), 299-306. Quadfasel, D., B. Rudels, and K. Kurz (1988), Outflow of dense water from a Svalbard fjord into the Fram Strait, Deep Sea Research Part A. Oceanographic Research Papers, 35(7), 1143-1150. Rudels, B., G. Bjork, J. Nilsson, P. Winsor, I. Lake, and C. Nohr (2005), The interaction between waters from the Arctic Ocean and the Nordic Seas north of Fram Strait and along the East Greenland Current: results from the Arctic Ocean-02 Oden expedition, Journal of Marine Systems, 55(1-2), 1-30. Sarnthein, M., S. van Krefeldt, H. Erlenkeuser, P. M. Grootes, M. Kucera, U. Pflaumann, and M. Schulz (2003), Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75◦N, Boreas, 32, 447-461

Enhanced modern heat transfer to the Arctic by warm Atlantic water

The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early–21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming