Holocene variability of surface and seep water advection to the Arctic Ocean - a multiproxy perspective from the aastern Fram Strait

Micropaleontological, geochemical, and sedimentological parameters of two sediment cores from the eastern Fram Strait have been studied to reconstruct the variability of surface and deep water advection and related fluctuations of the marginal ice zone during the past ca ∼9,000 years with multidecadal resolution. The Fram Strait between Greenland and Svalbard is the only deep connection between the Arctic and adjacent subpolar oceans and is often referred to as the ‘Arctic Gateway’. Fram Strait thus plays a crucial role for the energy budget and density pattern of the Arctic Ocean. Large amounts of warm and saline Atlantic Water derived from the North Atlantic Drift transport most of the heat through eastern Fram Strait to the Arctic basin, resulting in year-round ice-free conditions. Arctic sea ice and cold and fresh waters exit the western part of the strait southward along the Greenland shelf. Compared to the ice-covered Arctic Ocean, the strong east-west temperature gradient results in higher bioproductivity and sedimentation rates in the eastern Fram Strait which allows for suitably tracking Holocene variations of the heat flux to the Arctic Ocean in continuous high-resolution sediment sequences. The multiproxy results presented in this thesis suggest that the Holocene climate and oceanographic development in the Fram Strait and possibly the Arctic Ocean was much more variable than previously assumed. The variation and interaction between warm and saline advection of Atlantic Water at the surface to subsurface into the Arctic Ocean and a correspondingly fluctuating sea ice margin characterise the eastern Fram Strait throughout the Holocene. The data imply that the transition from deglacial/Early Holocene to modern-like conditions occurred stepwise. Inferred from the high relative abundance of the subpolar planktic foraminifer species Turborotalia quinqueloba, intense advection of warm Atlantic Water to the Arctic Ocean marks the Early and Mid-Holocene interval (~9,000 to 5,000 years before present), concurrent with high insolation at that time. Superimposed on optimum climate conditions, repeated cold events such as the well-known ‘8,200 year cold event’ are observed. These cold events are likely related to repeated advances of the sea ice margin and the Arctic freshwater layer. A roughly 550-year cyclicity of bottom water inflow, indicated by benthic carbon isotope data, coincide with North Atlantic bottom sediment proxy records and may suggest that deepwater variations in the Fram Strait were linked to changes in thermohaline convection processes in the Nordic Seas. Modern (pre-industrial) climate conditions evolved after 5,000 years before present, simultaneous to the decreasing insolation and postglacial sea level highstand which likely resulted in the onset of modern-like sea ice production on the shallow Siberian shelves. Dominance of the coldwater-indicating planktic foraminifer Neogloboquadrina pachyderma and a significantly increasing amount of ice rafted material point to a weaker and/or cool subsurface Atlantic Water inflow and advances of the Arctic Front during the Late Holocene Neoglacial phase. Strong southeastward advances of Arctic sea ice and polar water likely prevailed and caused heavy winter sea ice conditions and relatively short ice-free summer seasons in the eastern Fram Strait during this period. Distinct changes linked to the variable Atlantic Water inflow and fluctuations of the sea ice margin occurred during the past ~2,000 years. More stable conditions and reduced influence of the sea ice margin characterise the well-known Medieval Climate Anomaly. Subsequently, colder conditions mark the onset of the Little Ice Age period which occurred in two phases in the eastern Fram Strait. A first phase from ~1350 to 1750 AD was characterised by frequent shifts of the marginal ice zone, indicated by high amounts of ice rafted material and highly fluctuating planktic foraminifer fluxes. After ~1750 AD a second, very cold phase with heavy sea ice conditions established, concomitant with an increased abundance of icebergs from advancing Svalbard glaciers. Changes in all studied proxies in the uppermost sediment layer confirm a strong climate shift during the past few decades. Highest relative abundance of subpolar planktic foraminifer species in the uppermost sediment layer and the application of two independent temperature reconstruction methods reveal a temperature increase of ∼2°C within the past ∼120 years. Seawater-derived neodymium and lead isotope compositions stored in ferromanganese oxyhydroxide coatings of sediment particles were investigated to reconstruct Holocene variations of deep water exchanges between the Nordic Seas and the Arctic Ocean through Fram Strait. Inflow of deep waters from the Nordic Seas into the Arctic Ocean can clearly be deduced for the period between 9,000 and 3,000 years before present. Thereafter, coeval with the Neoglacial cooling trend in the northern North Atlantic region and the onset of modern Arctic sea ice production, significantly more radiogenic neodymium isotope compositions may be related to the enhanced release of ice rafted material in the eastern Fram Strait during the Late Holocene

Holocene episodes of warm conditions in the eastern Fram Strait - a multiproxy perspective on the variability of Atlantic Water inflow

EGU2011-2455 The current interglacial has gone through a variety of warmer and colder periods. Consistent with the decreasing solar insolation during the Holocene, warmest conditions have occurred particularly within its earliest phase. We studied high-resolution sediment sequences from the Western Svalbard margin covering the last ca 10,000 years in order to reconstruct the variations of Atlantic Water advection to the Arctic, the sea ice extent, and the structure of the water column on the Westspitsbergen continental margin. The Fram Strait, often referred to as the Arctic Gateway, is the only deep-water passage for Atlantic-derived water masses to enter the Arctic Ocean. Northward advection of relatively warm and saline Atlantic Water masses keeps the eastern part of the Fram Strait ice-free all year. It therefore plays a crucial role for the heat budget of the Arctic. A multiproxy data set including geochemical, micropaleontological, and sedimentological parameters was established with centennial to multidecadal time resolution. Records of foraminiferal oxygen and carbon isotopes, planktic foraminifer assemblages, and the amount of ice rafted debris clearly reveal distinct variations between climatically warmer and colder intervals throughout this period. Planktic foraminifer assemblages reveal warmest conditions for the early Holocene period (ca 10-8 ka). A second warming pulse is detected between 5 and 6 ka. In the second half of the Holocene, increased IRD contents are indicative of a significant cooling trend. Despite of the decreasing solar insolation planktic foraminiferal assemblages suggest a return of slightly strengthened Atlantic Water advection around 3 to 2 ka and a strong warming event in the present, anthropogenically influenced period

Neoglacial cooling culminates in rapid sea ice oscillations in eastern Fram Strait

EGU2011-407 The spatial and temporal distribution of sea ice in the subpolar North Atlantic is mainly controlled by the advection of warm Atlantic Water via the Norwegian and West Spitsbergen Current in eastern Fram Strait. Simultaneously, polar water and sea ice from the Arctic Ocean is transported southward by the East Greenland Current. Hence, variations in the strength of this oceanic circulation regime may either stimulate or reduce the sea ice extent. Based on organic geochemical studies of a high-resolution sediment core from eastern Fram Strait we provide new evidence for the highly variable character of the sea ice conditions in this area. The combination of the sea ice proxy IP25 (Belt et al., 2007) with phytoplankton derived biomarkers (e.g. brassicasterol, dinosterol; Volkman 2006) enables a reliable reconstruction of sea surface and sea ice conditions, respectively (Müller et al., 2009; 2010). By means of these biomarkers, we trace gradually increasing sea ice occurrences from the Mid to the Late Holocene – consistent with the neoglacial cooling trend. Throughout the past ca. 3,000 years (BP) we observe a significant short-term variability in the biomarker records, which points to rapid advances and retreats of the sea ice cover at the continental margin of West Spitsbergen. The co-occurrence of IP25 and phytoplankton markers, however, suggests that the primary productivity benefits from these sea ice surges. As such, higher amounts of open-water phytoplankton biomarkers together with peak abundances of IP25 indicate recurring periods of enhanced ice-edge phytoplankton blooms at the core site. To what extent a seesawing of temperate Atlantic Water may account for these sea ice fluctuations requires further investigation. Concurrent variations in Siberian river discharge (Stein et al., 2004) or Norwegian glacier extents (Nesje et al., 2001), however, strengthen that these fluctuations may be assigned to variations in the North Atlantic/Arctic Oscillation (NAO/AO) and (hence) a weakened/accelerated Atlantic Water input and Arctic sea ice export

Stepwise transition from deglacial/Early Holocene to modern-like conditions in the eastern Fram Strait, sub-Arctic north, inferred from planktic foraminifer fauna and sea surface temperatures

EGU2012-4750 The heat content of the Arctic Ocean is mainly controlled by the inflow of north-heading warm and saline Atlantic Water through eastern Fram Strait. The eastern Fram Strait is therefore ice-free all year, opposite to its perennially ice-covered western part where large amounts of Arctic sea ice are exported year-round to the Nordic Seas. The Early and Mid-Holocene phases (ca 12 to 5 cal ka BP) in the (sub-)Arctic have been especially marked not only by high summer insolation but also by rising sea level and the final disintegration of large ice sheets that had been established during the preceding glacial phase. Two sediment cores with multidecadal resolution from the Western Svalbard margin have been investigated for its planktic foraminiferal distribution, sea surface temperatures, planktic and benthic stable isotope ratios, and lithological parameters to derive information on the Holocene variability of the heat transport to the Arctic Ocean and related fluctuations of the marginal ice zone in the eastern Fram Strait. Planktic foraminifer fauna and a summer sea surface temperature reconstruction based on the modern analogue technique imply a stepwise transition from deglacial/Early Holocene to modern-like conditions in the eastern Fram Strait. Repeated short-term advances of the sea ice margin accompanied the generally strong heat transport to the Arctic Ocean during the Early to Mid-Holocene. Consistent with the decreasing solar insolation, cooler (sub-)surface conditions established after ca 5 cal ka BP most likely related to both a weakening of the Atlantic Water inflow and strong export of Arctic sea ice through Fram Strait. The Late Holocene Neoglacial phase was characterized by high contents of ice-rafted material and dominance of the cold water-indicating planktic foraminifer species Neogloboquadrina pachyderma. Cool Late Holocene conditions are reversed by a strong warming event likely caused by a significant strengthening of Atlantic heat advection to the Arctic during the present, anthropogenically influenced period

Holocene fluctuations of neodymium isotope ratios in eastern Fram Strait sediments - An indication for deepwater variability?

EGU2012-11739 The Fram Strait as the only deep water connection of the world’s oceans to the Arctic plays a substantial role for the heat influx to the Arctic Ocean and controls freshening of the Nordic Seas through Arctic sea ice export. Large amounts of warm and saline Atlantic Water derived from the North Atlantic Drift transport most of the heat through eastern Fram Strait to the Arctic basin, resulting in year-round ice-free conditions. Arctic sea ice and cold and fresh waters exit the western part of the strait southward along the Greenland shelf. However, little is still known about the water mass transport at intermediate and bottom water depths in the Fram Strait. High-resolution Holocene sediment sequences from the Western Svalbard margin have been investigated for its neodymium isotope ratios stored in ferromanganese oxyhydroxide coatings of the sediment to derive information on the source of bottom seawater passing the site. The radiogenic isotope data are compared to a multitude of proxy indicators for the climatic and oceanographic variability in the eastern Fram Strait during the past 8,500 years. In order to obtain a calibration of the Nd isotope compositions extracted from sediments to modern bottom water mass signatures in the area, a set of core top and water samples from different water depths in the Fram Strait was additionally investigated for its present-day Nd isotope signatures. A significantly higher inflow of deepwater produced in the Nordic Seas to the core site is inferred for the earlier periods of the Holocene. Cooler surface water conditions and increased sea ice abundances during the late Holocene coincide with more radiogenic Nd isotope ratios likely resembling the neoglacial trend of the northern North Atlantic

Im Austausch mit Forscher, Wetterexpertin und Kapitaen im internationalen Year of Polar Prediction

Ob es in den kommenden Tagen am Nordpol schneit, oder ob die Sonne scheint, ist ungewiss. Denn der Wetterbericht für die Arktis ist weitaus weniger verlässlich als für andere Regionen der Erde. Um die vorhandenen Lücken in den Vorhersagenkapazitäten für die Polargebiete zu schließen, hat die Weltorganisation für Meteorologie (WMO) im Jahr 2013 das zehnjährige Polar Prediction Project zur Verbesserung der Wetter- und Meereisvorhersagen für Arktis und Antarktis ins Leben gerufen. Eine wichtige Aufgabe des am Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung ansässigen Internationalen Koordinationsbüros besteht darin, mit Hilfe eines effektiven Kommunikationsmanagements einen erfolgreichen Wissenstransfer und –austausch zwischen den beteiligten Wissenschaftler/innen, den Expert/innen an den Wetterzentren und den Nutzer/innen von polaren Vorhersagen zu ermöglichen

MITOCHONDRIENFUNKTIONSSTÖRUNGEN BEI MYOPATHIEN UND DEGENERATIVEN ZNS-ERKRANKUNGEN

Als im Jahre 1890 erstmals kleine Organellen in einer Zelle beschrieben wurden, die in Größe und Form den Bakterien sehr ähnlich waren, wußte man noch nichts von der Bedeutung dieser sogenannten Mitochondrien. Zunehmend aber wurde erkannt, daß die Mitochondrien für bestimmte Stoffwechselprozesse zuständig sind, insbesondere für solche der Energiebereitstellung. Die Mitochondrienforschung der letzten Jahre förderte dazu bisher völlig unbekannte Eigenschaften zutage, die die Mitochondrien interessant machen im Hinblick auf den Zelltod, für die Vererbungslehre, für die klinische Medizin oder auch für die Gerichtsmedizin. Daß die Mitochondrien bis heute aktueller Forschungsgegenstand sind, beweist eindrucksvoll die Märzausgabe 1999 der hochrangigen internationalen Fachzeitschrift „Science“ (Abb. 1), in der der mitochondrialen Forschung sogar ein Comeback bescheinigt wird

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

Enhanced Atlantic water inflow warms the Arctic

Never in the last 2,000 years was the Atlantic Water entering the Arctic in the Fram Strait between Greenland and Svalbard as warm as today. This was revealed by a study of marine sediments from the western Svalbard continental margin which was led by researchers from IFM-GEOMAR