Reconstruction of Water Temperatures and Salinity
The reconstruction of environmental parameters by various indicators - a so called multiproxy approach (Fig. 2) - allows conclusions on the variability of Atlantic Water advection to the Arctic and the related northward heat transport. Therefore, long sediment cores from the continental margins of western and northern Svalbard (Fig. 1) are dated by the AMS-14C method and analyzed in high temporal resolution (decades to centennials) using sedimentological, micropaleontological, and geochemical methods.
From the relative abundance of subpolar and polar foraminifers (Protozoa; species from temperate and cold water masses, respectively; Fig. 2) we can reconstruct changes of water temperatures and the related movements of the ice margin. Oxygen and carbon isotope values of foraminifer shells allow conclusions on the salinity and structure of the water masses.
Contact: Dr. Robert F. Spielhagen
The Fram Strait between Greenland and Svalbard (Spitsbergen) is the major connection between the Arctic Ocean and the world ocean (Fig. 1). In its eastern part, relatively warm and saline water masses from the North Atlantic enter the Arctic. This current, the northernmost extension of the so-called "Gulf Stream", provides ice-free conditions in the waters west of Svalbard even in winter.
The heat transport by the North Atlantic Current is the primary factor influencing climate in central and northern Europe. To assess the ongoing rapid climate changes, it is therefore important to analyze the range of natural variability in heat transport at high resolution. The oceanic region between the ice-free eastern Nordic Seas and the ice-covered Arctic Ocean is particularly suitable for such reconstructions, because the sedimentary environments are strongly different and can be distinguished in sedimentary records. In the Fram Strait, between Svalbard and Greenland, we find strong oceanographic contrasts which play an important role in the global ocean circulation.
Recent temperature increase in the Fram Strait as unprecedented in past 2,000 years
Investigations of marine sediments from the eastern Fram Strait revealed that temperatures of the northward inflowing Atlantic Water varied several tenths of a degree Celsius during the past 2,000 years. The most recent temperature increase of approximately two degrees Celsius, however, is unprecedented in the past 2,000 years (Fig. 3). Such a warming of the Atlantic Water in the Fram Strait significantly differs from all climate variations in the past 2,000 years.
Because continuous meteorological and oceanographical data series extend only ~150 years into the past, natural climate archives like ice cores or sediment cores are used for investigations of past climate variability. In this study specific foraminifers from a sediment core were used to reconstruct water temperatures in the Fram Strait. These protozoans live in water depths of 50 to 200 metres and build calcareous shells. When they die, the shells sink and accumulate on the sea floor together with other particles (Fig. 2). Because specific foraminiferal species prefer specific water temperatures, the species associations in sediment samples of a known age can be used to determine past oceanic and climatic conditions.
In addition, the chemical composition of the calcareous shells was analyzed, which also allows reconstructing the water temperature in which the foraminifers lived. Using these two independent methods, several warmer and cooler intervals in the Fram Strait during the past 2,000 years were found (Fig. 3). One of these intervals was the 'Little Ice Age' from the mid-15th to the late 19th century when it was unusually cold. In contrast, unusually in the very youngest deposits many subpolar foraminifers, advected by warmer waters from the Atlantic, were found. Both methods applied show a temperature increase of approximately two degrees in the last 100 years (Fig. 3). Today, temperatures of the Atlantic Water in the Fram Strait are approximately 1.5 degrees higher than during the climatically warm early Medieval Period. The accelerated decrease of the Arctic sea ice cover and the warming of ocean and atmosphere in the Arctic, as measured during the past decades, may in part be related to an increased heat transfer from the Atlantic.
Further information about the HOVAG project (pdf file)
References
Spielhagen, R.F., K. Werner, S. Aagaard Sørensen, K. Zamelczyk, E. Kandiano, G. Budeus, K. Husum, T. M. Marchitto, M. Hald, 2011: Enhanced Modern Heat Transfer to the Arctic by Warm Atlantic Water. Science, 331, 450-453.
Werner, K., R.F. Spielhagen, D. Bauch, H.C. Hass, E. Kandiano, K. Zamelczyk, 2011: Atlantic Water advection to the eastern Fram Strait - Multiproxy evidence for late Holocene variability. Palaeo3, 308, 264 -276.
