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.

Distribution of planktic foraminifera in surface sediments and sedimentation rates of sediment cores from the Ibero-Moroccan continental rise and slope

Cores from the Atlantic Ibero-Moroccan continental rise and slope contain fine-grained Late Pleistocene and Holocene sediments. These young sediments cover the continental margin in large lensformed litho- and biostratigraphically well-defined units. The total sedimentation rates range from 4 cm/ 1000 yrs. to 27 cm/1000 yrs. off Portugal and from 6 cm/1000 yrs. to 14 cm/1000 yrs. off Morocco. Only a small proportion of these sediments usually consists of sand-sized particles (>0.063 mm) which are mostly dominated by foraminifera. Both planktonic and benthic foraminifera are much more abundant in Late Pleistocene and Holocene samples from the upper slope in comparison to those from the deeper slope and from the abyssal plains. Total sedimentation rates during cool and warm climatic stages are rather similar for both groups of foraminifera. For example, in Late Holocene sediments 7 x 10**3 benthic and 201 x 10**3 planktonic foraminifera (fraction 0.63 -0.20 mm) per 100 cm**2 and 1000 yrs. are preserved in the Tagus, 10-19 X 10**3 benthic and about 1.3 X 10**6 planktonic foraminifera are preserved in the Seine abyssal plain sediments. Values from the upper slope sediments are higher for benthic foraminifera by a factor of 60 off Portugal and 60 to 70 off Morocco. The values for planktonic ones differ by factors of 6-12 and 6 respectively. These numbers seem to reflect differences in production and preservation. Production rates of planktonic foraminifera generally seem to be somewhat higher during Holocene than during Late Pleistocene, and the rates of benthic foraminifera appear rather higher during Late Pleistocene than during Holocene.

Recent benthic foraminifera of the Scotia Sea and Argentine Basin

We investigated 88 surface sediment samples taken with a multiple corer from the southwestern South Atlantic Ocean for their live (Rose Bengal stained) and dead benthic foraminiferal content. Using Q-Mode Principal Component Analysis six live and six dead associations are differentiated. Live and dead association distributions correspond fairly well; differences are mainly caused by downslope transport and selective test destruction. In addition, four potential fossil associations are calculated from the dead data set after removal of non-fossilizable species. These potential fossil associations are expected to be useful for paleoceanographic reconstructions. Environments are described in detail for the live and potential fossil associations and for selected species. Along the upper Argentine continental slope strong bottom currents control the occurrence of live, dead and potential fossil Angulogerina angulosa associations. Here, particles of a high organic carbon flux rate remain suspended. Below this high energy environment live, dead and potential fossil Uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates. The live A. angulosa and U. peregrina associations correlate with high standing crops. Furthermore, live and dead Epistominella exigua-Nuttallides umbonifer associations were separated. Dominance of a Nuttallides umbonifer potential fossil association relates to coverage by Antarctic Bottom Water (AABW) and Lower Circumpolar Deep Water (LCDW), above the Calcite Compensation Depth (CCD). Three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by AABW or CDW. A Reophax difflugiformis association was found in mud-rich and diatomaceous sediments. Below the CCD, a Psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a Cribrostomoides subglobosus-Ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30%. One single Eggerella bradyi-Martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the CCD if only preservable species are considered for calculation.

Seawater carbonate chemistry and benthic foraminifera Ammonia sp. mass, size, and growth rate during experiments, 2013

About 30% of the anthropogenically released CO2 is taken up by the oceans; such uptake causes surface ocean pH to decrease and is commonly referred to as ocean acidification (OA). Foraminifera are one of the most abundant groups of marine calcifiers, estimated to precipitate ca. 50 % of biogenic calcium carbonate in the open oceans. We have compiled the state of the art literature on OA effects on foraminifera, because the majority of OA research on this group was published within the last three years. Disparate responses of this important group of marine calcifiers to OA were reported, highlighting the importance of a process-based understanding of OA effects on foraminifera. We cultured the benthic foraminifer Ammonia sp. under a range of carbonate chemistry manipulation treatments to identify the parameter of the carbonate system causing the observed effects. This parameter identification is the first step towards a process-based understanding. We argue that CO3 is the parameter affecting foraminiferal size-normalized weights (SNWs) and growth rates. Based on the presented data, we can confirm the strong potential of Ammonia sp. foraminiferal SNW as a CO3 proxy.

Diversity and faunal composition of benthic foraminifera in Hole 44-390A on the Blake Nose Plateau

Benthic foraminiferal assemblages are a widespread tool to understand changes in organic matter flux and bottom-water oxygenation and their relation to paleoceanographic changes in the Upper Cretaceous oceans. In this study, assemblage data (diversity, total number, and number per species and gram) from Deep Sea Drilling Project (DSDP) Site 390 (Blake Nose, western North Atlantic) were processed for the lower Maastrichtian (Globotruncana falsostuarti - Gansserina gansseri Planktic Foraminiferal Zone). These data document significant changes in nutrient flux to the sea floor as well as bottom-water oxygenation during this time interval. Parallel to the observed changes in the benthic foraminiferal assemblages the number of inoceramid shells decreases, reflecting also a significant increase in bottom-water oxygenation. We speculate, that these data could reflect the onset of a shift from warmer low-latitude to cooler high-latitude deep-water sources. This speculation will predate the major reorganization of the oceanic circulation resulting in a circulation mode similar to today at the Early/Late Maastrichtian boundary by ~1 Ma and therefore improves our understanding of Late Cretaceous paleoceanography.