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

Observing the oceanic heat flux toward retreating outlet glaciers in NE-Greenland

Warming of subsurface water of Atlantic origin has been suggested to be a major driver of the ongoing retreat of marine terminating glaciers around the coast of Greenland. In recent years, also the outlet glaciers of the Northeast Greenland Ice Stream have undergone major changes leading to an increased mass flux from the ice sheet into the ocean. Both, the thinning of the 80-km long floating tongue of the 79 North Glacier and the collapse of the floating tongue of the adjacent Zachariæ Isstrøm have been attributed to increasing ocean temperatures. However, it has been unclear whether the bathymetry was sufficiently deep to allow warm Atlantic water to reach Zachariæ Isstrøm. Here we report on the first station-based bathymetric and oceanographic measurements carried out in summers 2016 and 2017 close to the calving front of Zachariæ Isstrøm. They reveal 1°C-warm waters of Atlantic origin in a layer between 300 to 600-m depth to be in direct contact with the calving front of the glacier. Also, 12-month long mooring based observations demonstrate Atlantic origin waters to flush the cavity beneath the 79 North Glacier causing high basal melt rates along the 80-km-long glacier base. Based on moored measurements further offshore on the Northeast Greenland continental shelf we discuss the processes that govern the oceanic heat transport toward both glaciers. A better understanding of these processes is relevant to distinguish short-term variability from long-term changes in the oceanic heat flux toward the glaciers

From pole to pole : 33 years of physical oceanography onboard R/V Polarstern

Measuring temperature and salinity profiles in the world's oceans is crucial to understanding ocean dynamics and its influence on the heat budget, the water cycle, the marine environment and on our climate. Since 1983 the German research vessel and icebreaker Polarstern has been the platform of numerous CTD (conductivity, temperature, depth instrument) deployments in the Arctic and the Antarctic. We report on a unique data collection spanning 33 years of polar CTD data. In total 131 data sets (1 data set per cruise leg) containing data from 10 063 CTD casts are now freely available at doi: 10.1594/PANGAEA.860066. During this long period five CTD types with different characteristics and accuracies have been used. Therefore the instruments and processing procedures (sensor calibration, data validation, etc.) are described in detail. This compilation is special not only with regard to the quantity but also the quality of the data -the latter indicated for each data set using defined quality codes. The complete data collection includes a number of repeated sections for which the quality code can be used to investigate and evaluate long-term changes. Beginning with 2010, the salinity measurements presented here are of the highest quality possible in this field owing to the introduction of the OPTIMARE Precision Salinometer.Peer reviewe

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