Benthic foraminifera of late Quaternary sediments in the northern North Atlantic

Four long sediment cores from locations in the Framstrait, the Norwegian-Greenland Seas and the northern North Atlantic were analysed in a high resolution sampling mode (1 - 2 cm density) for their benthic foraminiferal content. In particular the impact of the intense climatic changes at glacial/interglacial transitions (terminations I and II) on the benthic community have been of special interest. The faunal data were investigated by means of multivariate analysis and represented in their chronological occurence. The most prominent species of benthic foraminifera in the Norwegian-Greenland Seas are Oridorsalis umbonatus, Cibicidoides wuellerstorfi, the group of Cassidulina, Pyrgo rotalaria, Globocassidulina subglobosa and fragmented tubes of arenaceous species. The climatic signal of termination I as well as termination II is recorded in the fossil foraminiferal tests as divided transition from glacial to interglacial. The elder INDAR maximum (individuals accumulation rate = individuals/sq cm * 1.000 y; Norwegian-Greenland Seas: average 3.000 - 6.000 individuals/sq cm * 1.000 y; northern North Atlantic: average 150 individuals/sq cm * 1.000 y) is followed by a period of decreased values. The second, younger maximum reaches comparable values as the elder maximum. The interglacial INDAR are in average 700 individuals/sq cm * 1.000 y in the Norwegian-Greenland Seas and 200 individuals/sq cm * 1.000 y in average in the northern North Atlantic. The occurence of the elder INDAR maximum shows a distinct chronological transgressivity between the northern North Atlantic (12.400 ybp.) and the Framstrait (8.900 ybp.). The time shift from south to north amounts 3.500 yrs., the average expanding velocity 0,78 km per year. Within the Norwegian-Greenland Seas the average expanding velocity amounts 0,48 km per year. This chronological transgressivity is interpreted as impact of the progressive expanding of the North Atlantic and the Norwegian Current during the deglaciation. The dynamic of the faunal development is defined as increasing INDAR per time. The elder INDAR maximum shows in both glacial/interglacial transitions an exponential increase from south to north. Termination II is characterized by a general higher dynamic as termination I. By means of the high resolution sampling density the impact of regional isotopic recognized melt-water events is recognized by an increase of endobenthic and t-ubiquitous species in the Norwegian-Greenland Seas sediments. During termination I the relative minimum between both INDAR maxima occur chronological with an decrease of calculated sea surface temperatures. This is interpreted as indication of the close pelagic - benthic coupling. The climatic signal in the northern North Atlantic recorded in the fossil benthic foraminiferal community shows a lower amplitude as in the Norwegian-Greenland Seas. The occurence of the epibenthic Cibicidoides wuellersforfi allows to evaluate the variability of the bottom water mass. In general at all core locations increasing lateral bottom currents are recognized with the occurence of the second younger INDAR maximum. In comparison with various paleo-climatological data sets fossil benthic foraminifers show a distinct koherence with changes of the atmospheric temperatures, the SSTs and the postglacial sea level increase. The benthic foraminiferal fauna is bound indirectly on and indicative for regional climatic changes, but principal dependent upon global climatic changes.

Sedimentology and benthic foraminiferal assemblages of the late Younger Dryas and early Holocene in the Skagerrak

A high-resolution study of palaeoenvironmental changes through the late Younger Dryas and early Holocene in the Skagerrak, the eastern North Atlantic, is based on multi-proxy analyses of core MD99-2286 combined with palaeo-water depth modelling for the area. The late Younger Dryas was characterized by a cold ice-distal benthic foraminiferal fauna. After the transition to the Preboreal (c. 11 650 cal. a BP) this fauna was replaced by a Cassidulina neoteretis dominated fauna, indicating the influence of chilled Atlantic Water at the sea floor. Persisting relatively cold bottom-water conditions until c. 10 300 cal. a BP are presumably a result of an outflow of glacial meltwater from the Baltic area across south-central Sweden, which develops a strong stratification of the water column at MD99-2286. A short-term peak in the C/N ratio at c. 10 200 cal. a BP is suggested to indicate input of terrestrial material, which may represent the drainage of an ice-dammed lake in southern Norway, the Glomma event. After the last drainage route across south-central Sweden closed, c. 10 300 cal. a BP, the meltwater influence diminished, and the Skagerrak resembled a fjord with stable inflow of waters from the North Atlantic through the Norwegian Channel and a gradual increase in boreal species. Full interglacial conditions were established at the sea floor from c. 9250 cal. a BP. Subsequent warm stable conditions were interrupted by a short-term cooling around 8300-8200 cal. a BP, representing the 8.2 ka event.

Vertical distribution of benthic foraminifers in the Arctic Ocean

The vertical distribution of living (Rose Bengal stained) benthic foraminifers was determined in the upper 15 cm of sediment cores taken along transects extending from the continental shelf of Spitsbergen through the Eurasian Basin of the Arctic Ocean. Cores taken by a multiple corer were raised from 50 stations with water depths between 94 and 4427 m, from areas with moderate primary production values to areas that are among the least productive ones in the world. We believe, that in the Arctic Ocean the vertical distribution of living foraminifers is determined by the restricted availability of food. Live foraminiferal faunas are dominated by potentially infaunal species or epifaunal species. Species confined to the infaunal microhabitat are absent in Arctic sediments that we examined, and predominantly infaunal living species are nowhere dominant. In general, an infaunal mode of life is restricted to the seasonally ice-free areas and thus to areas with at least moderate primary production during the summer period. Under the permanent ice cover living species are usually restricted to the top centimeter of the sediment surface, even though some are able to dwell deeper in the sediment under ice-free conditions.

Benthic foraminiferal record and age dating of sediment cores from the Gullmar Fjord at the west coast of Sweden

A high-resolution study of benthic foraminiferal assemblages was performed on a ca. eight metre long sediment core from Gullmar Fjord on the west coast of Sweden. The results of 210Pb- and AMS 14C-datings show that the record includes the two warmest climatic episodes of the last 1500 years: the Medieval Warm Period (MWP) and the recent warming of the 20th century. Both periods are known to be anomalously warm and associated with positive NAO winter indices. Benthic foraminiferal successions of both periods are compared in order to find faunal similarities and common denominators corresponding to past climate changes. During the MWP, Adercotryma glomerata, Cassidulina laevigata and Nonionella iridea dominated the assemblages. Judging from dominance of species sensitive to hypoxia and the highest faunal diversity for the last ca. 2400 years, the foraminiferal record of the MWP suggests an absence of severe low oxygen events. At the same time, faunas and d13C values both point to high primary productivity and/or increased input of terrestrial organic carbon into the fjord system during the Medieval Warm Period. Comparison of the MWP and recent warming revealed different trends in the faunal record. The thin-shelled foraminifer N. iridea was characteristic of the MWP, but became absent during the second half of the 20th century. The recent Skagerrak-Kattegat fauna was rare or absent during the MWP but established in Gullmar Fjord at the end of the Little Ice Age or in the early 1900s. Also, there are striking differences in the faunal diversity and absolute abundances of foraminifera between both periods. Changes in primary productivity, higher precipitation resulting in intensified land runoff, different oxygen regimes or even changes in the fjord's trophic status are discussed as possible causes of these faunal differences.

Distribution of diatom species as abundance estimates from vertical multinet hauls from 150 m water depth in the Indian Ocean

During the Indian Ocean Expedition of R/V METEOR phytoplankton samples were taken with a multiple closing net (Multinet) at 103 stations. In this material the diatoms were investigated. In all 247 taxa could be identified which belong to 242 species and 5 varieties of formae of 80 genera. Of these 1 variety, 15 pecies, and 3 genera are newly described. New combinations were made for 18 species, and a number of old combinations was reinstated.