Benthic foraminiferal record from Santa Barbara basin

The oxygen minimum zone (OMZ) of the late Quaternary California margin experienced abrupt and dramatic changes in strength and depth in response to changes in intermediate water ventilation, ocean productivity, and climate at orbital through millennial time scales. Expansion and contraction of the OMZ is exhibited at high temporal resolution (107-126 year) by quantitative benthic foraminiferal assemblage changes in two piston cores forming a vertical profile in Santa Barbara Basin (569 m, basin floor; 481 m, near sill depth) to 34 and 24 ka, respectively. Variation in the OMZ is quantified by new benthic foraminiferal groupings and new dissolved oxygen index based on documented relations between species and water-mass oxygen concentrations. Foraminiferal-based paleoenvironmental assessments are integrated with principal component analysis, bioturbation, grain size, CaCO3, total organic carbon, and d13C to reconstruct basin oxygenation history. Fauna responded similarly between the two sites, although with somewhat different magnitude and taxonomic expression. During cool episodes (Younger Dryas and stadials), the water column was well oxygenated, most strongly near the end of the glacial episode (17-16 ka; Heinrich 1). In contrast, the OMZ was strong during warm episodes (Bølling/Allerød, interstadials, and Pre-Boreal). During the Bølling/Allerød, the OMZ shoaled to <360 m of contemporaneous sea level, its greatest vertical expansion of the last glacial cycle. Assemblages were then dominated by Bolivina tumida, reflecting high concentrations of dissolved methane in bottom waters. Short decadal intervals were so severely oxygen-depleted that no benthic foraminifera were present. The middle to late Holocene (6-0 ka) was less dysoxic than the early Holocene.

Stable isotope record, foraminifera and susceptibility determination of sediment core ENAM93-21

A high-resolution piston core, ENAM93-21, from a water depth of 1020 m near the Faeroe-Shetland Channel is investigated for variations in magnetic susceptibility, surface oxygen isotopes, grain size distribution, content of ice-rafted detritus (IRD), and distribution of planktonic and benthic foraminifera. The core, covering the last 58,000 years, is correlated with the Greenland ice cores and compared with paleorecords from the Norwegian Sea and the North Atlantic Ocean. All fifteen Dansgaard-Oeschger climatic cycles recognized from the investigated time period in the Greenland ice cores have been identified in the ENAM93-21 core. Each cycle is subdivided into three intervals on the basis of characteristic benthic and planktonic faunas. Interstadial intervals contain a relatively warm planktonic fauna and a benthic fauna similar to the modern fauna in the Norwegian Sea. This indicates thermohaline convection as at present, with a significant contribution of deep water to the North Atlantic Deep Water (NADW). Transitional cooling intervals are characterized by more cold water planktonic foraminfera and ice-related benthic species. The benthic fauna signifies restricted bottom water conditions and a reduced contribution to the NADW. The peak abundance of N. pachyderma (s.) and the coldest surface water conditions are found in the stadial intervals. The benthic fauna is dominated by species with an association to Atlantic Intermediate Water, suggesting an increased Atlantic influence in the Norwegian Sea, and there was probably no contribution to the NADW through the Faeroe-Shetland Channel. The three different modes of circulation can be correlated to paleoceanographic events in the Norwegian Sea and the North Atlantic Ocean.

Paleotemperature and productivity reconstruction of sediment core D11957P on the Iberian Margin

Foraminifera counts and climatic assemblages from the Tore Seamount are used to approach the glacial and interglacial changes in temperature and productivity on the Iberian Margin over the last 225 kyr. Chronostratigraphy is based on Globigerinoides ruber and Globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations. Foraminifera indicate cooling from late interglacial stage 5 to the beginning of Termination I (TI). Neogloboquadnna pachyderma-s reflects cold conditions during glacial stages 4-2. In contrast, glacial stage 6 is dominated by warmer N. pachyderma-d and dutertrei and a restricted arctic assemblage. Past sea surface temperatures confirm the general cooling, reaching 4.3°C (SIMMAX.28) during stage 2. Multiple productivity proxies such as organic carbon, productivity-related foraminifera, and delta13C constrain the changes observed. A productivity increase occurs after interglacial stage 5, enhanced from late glacial stage 3 to TI Present-day satellite-detected phytoplankton plumes off Portugal would have accounted in the past glacial stages for the general productivity increase over the Tore. On top of this, welldefined peaks of organic carbon and productivity-related foraminifera correspond with Heinrich events 1-4.

Extractions and analyses of reactive phosphorus in the Bering Sea from IODP Holes 323-U1341A and 323-U1341B

To reconstruct the cycling of reactive phosphorus (P) in the Bering Sea, a P speciation record covering the last ~ 4 Ma was generated from sediments recovered during Integrated Ocean Drilling Program (IODP) Expedition 323 at Site U1341 (Bowers Ridge). A chemical extraction procedure distinguishing between different operationally defined P fractions provides new insight into reactive P input, burial and diagenetic transformations. Reactive P mass accumulation rates (MARs) are ~ 20-110 µmol/cm2/ka, which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings. We find that authigenic carbonate fluorapatite (CFA) and opal-bound P are the dominant P fractions at Site U1341. An overall increasing contribution of CFA to total P with sediment depth is consistent with a gradual "sink switching" from more labile P fractions (fish remains, Fe oxides, organic matter) to stable authigenic CFA. However, the positive correlation of CFA with Al content implies that a significant portion of the supposedly reactive CFA is non-reactive "detrital contamination" by eolian and/or riverine CFA. In contrast to CFA, opal-bound P has rarely been studied in marine sediments. We find for the first time that opal-bound P directly correlates with excess silica contents. This P fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long-term sink for reactive P in the ocean, despite the likelihood for diagenetic re-mobilisation of this P at depth (indicated by increasing ratios of excess silica to opal-bound P). Average reactive P MARs at Site U1341 increase by ~ 25% if opal-bound P is accounted for, but decrease by ~ 25% if 50% of the extracted CFA fraction (based on the lowest CFA value at Site U1341) is assumed to be detrital. Combining our results with literature data, we present a qualitative perspective of terrestrial CFA and opal-bound P deposition in the modern ocean. Riverine CFA input has mostly been reported from continental shelves and margins draining P-rich lithologies, while eolian CFA input is found across wide ocean regions underlying the Northern Hemispheric "dust belt". Opal-bound P burial is important in the Southern Ocean, North Pacific, and likely in upwelling areas. Shifts in detrital CFA and opal-bound P deposition across ocean basins likely occurred over time, responding to changing weathering patterns, sea level, and biogenic opal deposition.

Distribution of meiobenthos in sediment samples of the northeastern Atlantic

The meiofauna of the deep sea areas (800 - 5500 m) between Madeira and Lisbon was quantitatively investigated during "Meteor" cruises in 1970 and 1971. With respect to numbers and biomass the meiofauna (especially nematodes and harpacticoid copepods) of the investigated areas is relatively poor averaging about 66,000 individuals per m**2 and 34 mg per m**2 wet weight biomass (polychaetes and foraminifera excluded). Regional differences are more pronounced in the investigated areas than differences due to depth. A comparison with the results of other authors from other areas confirms the regional variations in the meiofauna abundance of the deep sea.

Granulometry, geochemistry, amino acids, radiocarbon ages and paleomagnetics of samples from Heidemann Valley

A Pliocene (2.6-3.5 Ma) age is determined from glacial sediments studied in a 20m long, 4 m deep trench excavated in Heidemann Valley, Vestfold Hills, East Antarctica. The age determination is based on a combined study of amino acid racemization, diatoms, foraminifera, and magnetic polarity, and supports earlier estimates of the age of the sedimentary section; all are beyond 14C range. Four till units are recognized and documented, and 16 subunits are identified. All are ascribed to deposition during a Late Pliocene glaciation that was probably the last time the entire Vestfold Hills was covered by an enlarged East Antarctic Ice Sheet (EAIS). Evidence for other more recent glacial events of the 'Vestfold Glaciation' may have been due to lateral expansion of the Sorsdal Glacier and limited expansion of the icesheet margin during the Last Glacial Maximum rather than a major expansion of the EAIS. The deposit appears to correlate with a marine deposition event recorded in Ocean Drilling Program Site 1166 in Prydz Bay, possibly with the Bardin Bluffs Formation of the Prince Charles Mountains and with part of the time represented in the ANDRILL AND-1B core in the Ross Sea.

Calcareous nannofossils and C37 alkenones at ODP Site 162-982

During the late Pliocene (~3 to 2.5 Ma), oceanic records of opal and C37 alkenone accumulation from around the world show a secular shift towards lower values in the high latitudes and higher values in the low and mid latitudes. These shifts are broadly coincident with the intensification of northern hemisphere glaciation and are suggestive of changes in export productivity, with potential implications for Pliocene atmospheric carbon dioxide concentrations. The interpretation of a global latitudinal shift in productivity, however, requires testing because of the potential uncertainties associated with site to site comparisons of records that can be influenced by highly nonlinear processes associated with production, export, and preservation. Here, we assess the inferred Pliocene latitudinal productivity shift interpretation by presenting new records of C37 alkenone accumulation from Ocean Drilling Program (ODP) Site 982 in the North Atlantic and biotic assemblages (calcareous nannoplankton) from this site and ODP Site 846 in the eastern tropical Pacific. Our results corroborate the interpretation of C37 alkenone accumulation as a proxy for gross export productivity at these sites, indicating that large-scale productivity decreases at high latitudes and increases at tropical sites are recorded robustly. We conclude that the intensification of northern hemisphere glaciation during the late Pliocene was associated with a profound reorganisation of ocean biogeochemistry.

Pollen and macrofossil profiles from six cores in Illinois, U.S.A

Pollen analysis of Wisconsinan sediments from eleven localities in northern and central Illinois, combined with the results of older studies, allows a first general survey of the vegetational changes in Illinois during the last glaciation. In the late Altonian (after 40,000 B.P.), pine was already the most prevalent tree type in northern Illinois. Probably because of the influence of the last Altonian ice advance to northern Illinois, pine migrated to the south and reached south-central Illinois, which was at that time a region of prairie, with oak and hickory trees in favorable sites. Likewise in the late Altonian, spruce appeared in northern Illinois. Spruce also expanded its area to the south during the Wisconsinan, reaching south-central Illinois only after 21,000 B.P., in the early Woodfordian. Deciduous trees (predominantly oak) were present in south-central Illinois throughout the Wisconsinan. Their prevalence decreased to the north. The vegetation during the different subdivisions of the last glacial period in Illinois was approximately as follows: Late Altonian: Pine/spruce forest with some deciduous trees in northern and central Illinois; prairie and oak/hickory stands in south-central Illinois; immigration of pine. Farmdalian: Pine/spruce forest in central Illinois; deciduous trees and pine in south-central Illinois, with areas of open vegetation, perhaps similar to the present-day transition of prairie to forest in the northern Great Plains. Woodfordian: Northern and central Illinois ice covered; in south central Illinois, spruce and oak as dominant tree types, but also pine and grassland. During the Woodfordian, pine and spruce disappeared again from south-central Illinois, and oak/hickory forest and prairie again prevailed. The ice-free areas of northern Illinois become populated temporarily with spruce, but later there is proof of deciduous forest in this region. Pollen investigations in south-central Illinois have shown convincingly that deciduous trees could survive relatively close (less than 60 km) to the ice margin. Therefore the frequently presented view that arctic climatic conditions prevailed in North America during the last glaciation far south of the ice margin can be refuted for the Illinois area, confirming the opinion of other authors resulting from investigations of fossil mollusks and frost-soil features. The small number of localities investigated still permits no complete reconstruction of the vegetation zones and their possible movements in Illinois. During the Altonian and Farmdalian in Illinois, a vegetational zonation probably existed similar to that of today in North America. As the ice pushed southward as far as 39° 20' N. lat in the early Woodfordian, this zonation was apparently broken up under the influence of a relatively moderate climate. In any case, the Vandalia area, which was only about 60 km south of the ice, was at that time neither in a tundra zone nor in a zone of boreal coniferous forest.

Age determinations on sediment cores from the North Atlantic

Sediments in the North Atlantic ocean contain as eries of layers that are rich in ice-rafted debris and unusally poor in foraminifera. Here we present evidence that the most recent six of the 'Heinrich layers', deposited between 14,000 and 70,000 years ago, record marked decreases in sea surface temperature and salinity, decreases in the flux of planktonic forminifera to the sediments, and short-lived, massive discharges of icebergs originating in eastern Canada. The path of the icebergs, clearly marked by the presence of ice-rafted detrital carbonate, can be traced for more than 3,000 km - a remarkable distance, attesting to extreme cooling of surface waters and enormous amounts of drifiting ice. The cause of these extreme events is puzzling. They may reflect repated rapid advances of the Laurentide ice sheet, perhaps associated with reductions in air temperatures, yet temperature records from Greenland ice cores appear to exhibit only a weak corresponding signal. Moreover, the 5-10,000-yr intervals between the events are inconsistent with Milankovitch orbital periodicities, raising the question of what the ultimate cause of the postulated cooling may have been.

Planktic foraminifera analyses of surface sediments and satellite data in the Canary Islands region

The Canary Islands region occupies a key position with respect to biogeochemical cycles, with the zonal transition from oligotrophic to nutrient-rich waters and the contribution of Saharan dust to the particle flux. We present the distribution of geochemical proxies (TOC, carbonate, d15N, d13Corg, C/N-ratio) and micropaleontological parameters (diatoms, dinoflagellates, foraminifera, pteropods), in 80 surface-sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre. Results of the surface-sediment analyses confirmed the high biomass gradient from the coast to the open ocean inferred from satellite data of surface chlorophyll or SST. The distribution of total dinoflagellate cysts, the planktic foraminifera species Globigerina bulloides, the diatom resting spore Chaetoceros spp., and TOC concentration coincided well with the areas of strong filament production off Cape Ghir and Cape Yubi. The warm-water planktic foraminifera Globigerinoides ruber (white), the diatom Nitzschia spp., and the d15N-values showed the opposite trend with high values in the open ocean. Factor analyses on the planktic foraminifera species distribution indicated three major assemblages in the Canary Islands region that represent the present surface-water conditions from the upwelling influenced region via a mixing area towards the subtropical gyre.

Age model and pollen analysis from site GIK16867 in the northern Angola Basin

Sporomorphs and dinoflagellate cysts from site GIK16867 in the northern Angola Basin record the vegetation history of the West African forest during the last 700 ka in relation to changes in salinity and productivity of the eastern Gulf of Guinea. During most cool and cold periods, the Afromontane forest, rather than the open grass-rich dry forest, expanded to lower altitudes partly replacing the lowland rain forest of the borderlands east of the Gulf of Guinea. Except in Stage 3, when oceanic productivity was high during a period of decreased atmospheric circulation, high oceanic productivity is correlated to strong winds. The response of marine productivity in the course of a climatic cycle, however, is earlier than that of wind vigour and makes wind-stress-induced oceanic upwelling in the area less likely. Monsoon variation is well illustrated by the pollen record of increased lowland rain forest that is paired to the dinoflagellate cyst record of decreased salinity forced by increased precipitation and run-off.

Pollen flux off Cape Blanc

Fluxes of airborne freshwater diatoms (FD), phytoliths (PH), and pollen grains (PO) collected with sediment traps off Cape Blanc, northwest Africa, from 1988 till 1991 are presented. Both continental rainfall variations and wind mean strength and direction play a key role in the temporal fluctuations of the fluxes of eolian traces in the pelagic realm. Drier conditions in Northern Africa in 1987 could have preceded the high lithogenic input and moderate FD flux in 1988. The PH peak in summer 1988 was probably caused by increased wind velocity. Wetter rainy seasons of 1988/89 might have promoted a significant pollen production in summer 1989, and FD in late 1989 and early 1990, as well as contributed to the reduction of the lithogenic flux in 1989/90. Decreased fluxes of FD, PH and PO, and higher contribution of the 6-11 µm lithogenic fraction in 1991 would mainly reflect minor intensity and decreased amount of continental trade winds. Air-mass backward trajectories confirm that the Saharan Air Layer is predominantly involved in the spring/summer transport. Trade winds play a decisive role in the fall/winter months, but also contribute to the transport during late spring/summer. Origin of wind trajectories does not support a direct relationship between transporting wind-layers and material source areas in Northern Africa. High winter fluxes of eolian tracers and high amount of trade winds with continental origin in summer warn against a simplistic interpretation of the seasonal eolian signal preserved in the sediments off Cape Blanc, and the wind layer involved in its transport.

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.

Pollen analyses of sediment core GeoB1711-4 in the eastern South Atlantic

Influx of aeolian pollen trapped in marine sediments off Namibia provides a wind variation record for the last 135 kyr. The influx of major pollen components is derived from the southwest African desert/semi-desert zone and shows six periods during which enhanced southeast trade winds contributed to strong upwelling and reduced sea surface temperatures. The most prominent of these occurred during 17-23 cal. kyr, 42-56 kyr and before 130 kyr B.P. Correspondence between the pollen influx record and the Vostok deuterium isotope record suggests that pronounced glacial Antarctic cooling was accompanied by intensification of the southeast trades throughout the Late Quaternary. However, during 42-23 kyr B.P. the combination of strong Antarctic glaciation with a decrease of wind zonality induced by low latitude precessional insolation changes caused strong alongshore winds and Ekman pumping that resulted in strong upwelling and reduced sea surface temperatures without pollen influx enhancement.

Oligocene to early Miocene benthic foraminifera in the eastern Equatorial Pacific

We investigated Oligocene and early Miocene benthic foraminiferal faunas (> 105 µm in size) from Ocean Drilling Program (Leg 199) Site 1218 (4826 m water depth and ~3300 to ~4000 m paleo-water depth) and Site 1219 (5063 m water depth and ~4200 to ~4400 m paleo-water depth) to understand the response of abyssal benthic foraminifera to mid-Oligocene glacial events in the eastern Equatorial Pacific Ocean. Two principal factor assemblages were recognized. The Factor 1 assemblage (common Nuttallides umbonifer) is related to either an influx of the Southern Component Water (SCW), possibly carbonate undersaturated, or a decrease in seasonality of the food supply from the surface ocean. The Factor 2 assemblage is characterized by typical deep-sea taxa living under variable trophic conditions, possibly with a seasonal component in food supply. The occurrence of abyssal benthic foraminifera faunas during the mid-Oligocene depends on either the effect of SCW or the seasonality of food resources. The Factor 1 assemblage was most common near 76Ol-C11r, 73Ol-C10rn and 67Ol-C9n (ca. 30.2, 29.1 and 26.8 Ma respectively by Pälike et al. (2006, doi:10.1126/science.1133822)). This indicates that the effect of SCW increased or the seasonal input of food from the surface ocean to benthic environments was weakened close to these glacial events. In contrast, the huge export flux of small biogenic carbonate particles close to these glacial events might be responsible for carbonate-rich sediments buffering carbonate undersaturation. Changes in deep-water masses or the periodicity of food supply from the surface ocean and variation in surface carbonate production affected by orbital forcing had an impact on the mid-Oligocene faunas of abyssal benthic foraminifera around the intervals of glacial events in the eastern Equatorial Pacific Ocean. The Factor 1 assemblage decreased sharply at ? 30 Ma (29.8 Ma by Pälike et al. (2006), 30.0 Ma by CK95) and returned to dominance after ? 29 Ma (28.6 Ma by Pälike et al. (2006), 28.8 Ma by CK95). It is likely that the effect of SCW (possibly carbonate undersaturated) has intensified since the late Oligocene. The faunal transition of benthic foraminifera in the eastern Equatorial Pacific Ocean at ~29 Ma might be attributable to the influence of Northern Component Water (NCW) input to the Southern Ocean and the subsequent formation of SCW at about that time.