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

Surface ocean temperatures in the Northeast Atlantic during the last 500,000 years : Evidence from foraminiferal census data

Changes in North Atlantic sea surface temperature (SST) are regarded as a key element of the climate during the Quaternary. However, there are relatively few long-term records providing quantitative SST estimates from this region. Using planktic foraminiferal-derived SSTs together with changes on species level and iceberg-rafted debris, the last 500 ka were studied. Pronounced SST changes, as determined from the last glacial–interglacial cycle, characterize most colder periods. Peak interglacial temperatures were found for marine isotope stages (MIS) 1, 5e and 11, the latter two being the warmest. The warm substages within MIS 7 and 9 are marked by enhanced dissimilarity coefficients, indicating that SSTs obtained for these times appear to be overestimated. This is corroborated by differences within the species assemblage, which show enhanced cold water components. It is therefore concluded that detailed analysis down to species level is a crucial prerequisite to better reconstructions of SST

Contrasting ocean changes between the subpolar and polar North Atlantic during the past 135 ka

Variations in the poleward-directed Atlantic heat transfer was investigated over the past 135 ka with special emphasis on the last and present interglacial climate development (Eemian and Holocene). Both interglacials exhibited very similar climatic oscillations during each preceding glacial terminations (deglacial TI and TII). Like TI, also TII has pronounced cold–warm–cold changes akin to events such as H1, Bølling/Allerød, and the Younger Dryas. But unlike TI, the cold events in TII were associated with intermittent southerly invasions of an Atlantic faunal component which underscores quite a different water mass evolution in the Nordic Seas. Within the Eemian interglaciation proper, peak warming intervals were antiphased between the Nordic Seas and North Atlantic. Moreover, inferred temperatures for the Nordic Seas were generally colder in the Eemian than in the Holocene, and vice versa for the North Atlantic. A reduced intensity of Atlantic Ocean heat transfer to the Arctic therefore characterized the Eemian, requiring a reassessment of the actual role of the ocean–atmosphere system behind interglacial, but also, glacial climate changes. Key Points - Reduced AMOC during the Eemian - BA/YD-type warming/cooling in Termination 1 and 2 - Comparison of glacial inceptions reveals present climate statu

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

Uniform climate development between the subtropical and subpolar Northeast Atlantic across marine isotope stage 11

Proxy records from a core site off Northwest Africa were generated and compared with data from the subpolar Northeast Atlantic to unravel some main climatic features of interglacial marine isotope stage (MIS) 11 (423–362 ka). The records point to an almost 25 kyr lasting full interglacial period during stage 11 that was preceded by a considerably long glacial-interglacial transition (Termination V). Off NW Africa, a strong reduction of terrestrially derived iron input is noted after 420 ka suggesting a pronounced increase in continental humidity and vegetation cover over Northwest Africa. In analogy to the Holocene climate of the region, this early wet phase of MIS 11 was likely associated with enhanced influence of the West African monsoon system on the Saharan-Sahel region which led to both a reduction in trade wind intensity off NW Africa and the formation of sapropel S11 in the Mediterranean Sea. A detailed comparison with data from the subpolar North Atlantic indicates a remarkable coherent timing for the main environmental changes in both regions giving evidence for strong interglacial climate connection between the low and high latitude North Atlantic. Although our records of MIS 11 compare well with the Holocene in terms of some major climate characteristics there are distinct differences in the temporal evolution of each peak warm interval. This suggests that care should be taken when using MIS 11 as analogue to forecast future interglacial conditions

A cold and fresh ocean surface in the Nordic Seas during MIS 11: Significance for the future ocean

Paleoceanographical studies of Marine Isotope Stage (MIS) 11 have revealed higher-than-present sea surface temperatures (SSTs) in the North Atlantic and in parts of the Arctic but lower-than-present SSTs in the Nordic Seas, the main throughflow area of warm water into the Arctic Ocean. We resolve this contradiction by complementing SST data based on planktic foraminiferal abundances with surface salinity changes using hydrogen isotopic compositions of alkenones in a core from the central Nordic Seas. The data indicate the prevalence of a relatively cold, low-salinity, surface water layer in the Nordic Seas during most of MIS 11. In spite of the low-density surface layer, which was kept buoyant by continuous melting of surrounding glaciers, warmer Atlantic water was still propagating northward at the subsurface thus maintaining meridional overturning circulation. This study can help to better constrain the impact of continuous melting of Greenland and Arctic ice on high-latitude ocean circulation and climate

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

Sea surface temperature variability in the North Atlantic during the last two glacial-interglacial cycles: comparison of faunal, oxygen isotopic, and Mg/Ca-derived records

Climate variability in the northeast Atlantic was investigated on glacial–interglacial and millennial time scales during the last 200 000 years, using sea surface temperature (SST) records derived from planktonic foraminiferal diversities and from Mg/Ca measurements on Globigerina bulloides. Paleoceanographical interpretations are supported by species composition analyses, benthic and planktonic isotopic data as well as records of iceberg-rafted debris (IRD). Differences of climate development are recognized for both interglacial and glacial periods. Temperature estimates indicate slightly warmer conditions (up to 2°C) during marine oxygen isotope stage (MIS) 5e than during the Holocene. In contrast to the last glaciation, when the SST minimum coincided with a minimum in solar insolation immediately before Termination I, during the penultimate glaciation a long SST minimum occurred at times of intermediate solar insolation well preceding the onset of Termination II. This discrepancy between two glacial terminations may be explained by an inherently different orbital configuration characteristic for each glacial interval. Despite these differences between the two glacial trends, the superimposed shorter-lived climatic events reveal the same order of principal steps, implying their common causal nature. A direct comparison of faunal SSTs with those retrieved from Mg/Ca analysis shows that Mg/Ca-derived temperatures follow the general glacial–interglacial trend; however, the latter appear to be largely overestimated. Supported by δ18O data in G. bulloides, which show little response to millennial-scale variability, there seems to be a need for species-dependent calibration experiments that also consider the different oceanographic settings this particular species can live in