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.

Age model and sedimentation rate of core M174/KL11 (Table 1)

Stable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive delta18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53 per mil and 55 per mil are inferred from pteropod and benthic foraminifera delta18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic delta18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates.

Stable isotopes, PCBs and pesticide concentrations in zooplankton, seawater and POM from Kongsfjorden and Liefdefjorden, Svalbard

Differences in bioaccumulation of persistent organic pollutants (POPs) between fjords characterized by different water masses were investigated by comparing POP concentrations, patterns and bioaccumulation factors (BAFs) in seven species of zooplankton from Liefdefjorden (Arctic water mass) and Kongsfjorden (Atlantic water mass), Svalbard, Norway. No difference in concentrations and patterns of POPs was observed in seawater and POM; however higher concentrations and BAFs for certain POPs were found in species of zooplankton from Kongsfjorden. The same species were sampled in both fjords and the differences in concentrations of POPs and BAFs were most likely due to fjord specific characteristics, such as ice cover and timing of snow/glacier melt. These confounding factors make it difficult to conclude on water mass (Arctic vs. Atlantic) specific differences and further to extrapolate these results to possible climate change effects on accumulation of POPs in zooplankton. The present study suggests that zooplankton do biomagnify POPs, which is important for understanding contaminant uptake and flux in zooplankton, though consciousness regarding the method of evaluation is important.

Geochemistry of surface sediment cores (Table 4)

The mineralogy and geochemistry of a suite of nine manganese nodules from the South Atlantic have been determined. The Ce/La ratios of the nodules were investigated to see if they could be used as redox indicators to trace the oxygen content of the ambient water mass and the flow path of the Antarctic Bottom Water as has previously been successfully carried out in the Pacific Ocean. The Ce/La ratios of the nodules decrease in the sequence Lazarev Sea, Weddell Sea (10.4 and 9.7)>East Georgia Basin (6.5 and 7.1)>Argentine Basin (5.0), but then increase in the Brazil Basin (6.2) and Angola Basin (9.8 and 15.1). A further decrease was observed in the Cape Basin (7.6). An extremely high Ce/La ratio of 24.4 had already been determined for nodules sampled north of the Nares Abyssal Plain in the western North Atlantic. These data reflect the more complicated pattern of bottom water flow in the South Atlantic than in the South Pacific. The penetration of more oxygenated North Atlantic Deep Water into the South Atlantic accounts for the higher Ce/La ratios in the nodules from the Angola and Brazil basins. Based on this study, the flow path of the Antarctic Bottom Water could only be traced as far north as the Argentine Basin. The unique geochemistry of nodules from the central Angola Basin (high Mn/Fe and Ce/La ratios, high contents of Ni, Cu, Zn and Mo) appears to be a function of the nature of the overlying water mass and of the multiple diagenetic sources of metals to the nodules.

Standing stocks and carbon isotopes of live benthic foraminifera from the South Atlantic

Live (Rose Bengal stained) and dead benthic foraminifera of surface and subsurface sediments from 25 stations in the eastern South Atlantic Ocean and the Atlantic sector of the Southern Ocean were analyzed to decipher a potential influence of seasonally and spatially varying high primary productivity on the stable carbon isotopic composition of foraminiferal tests. Therefore, stations were chosen so that productivity strongly varied, whereas conservative water mass properties changed only little. To define the stable carbon isotopic composition of dissolved inorganic carbon (d13CDIC) in ambient water masses, we compiled new and previously published d13CDIC data in a section running from Antarctica through Agulhas, Cape and Angola Basins, via the Guinea Abyssal Plain to the Equator. We found that intraspecific d13C variability of all species at a single site is constantly low throughout their distribution within the sediments, i.e. species specific and site dependent mean values calculated from all subbottom depths on average only varied by +/-0.09 per mil. This is important because it makes the stable carbon isotopic signal of species independent of the particular microhabitat of each single specimen measured and thus more constant and reliable than has been previously assumed. So-called vital and/or microhabitat effects were further quantified: (1) d13C values of endobenthic Globobulimina affinis, Fursenkoina mexicana, and Bulimina mexicana consistently are by between -1.5 and -1.0 per mil VPDB more depleted than d13C values of preferentially epibenthic Fontbotia wuellerstorfi, Cibicidoides pachyderma, and Lobatula lobatula. (2) In contrast to the Antarctic Polar Front region, at all stations except one on the African continental slope Fontbotia wuellerstorfi records bottom water d13CDIC values without significant offset, whereas L. lobatula and C. pachyderma values deviate from bottom water values by about -0.4 per mil and -0.6 per mil, respectively. This adds to the growing amount of data on contrasting cibicid d13C values which on the one hand support the original 1:1-calibration of F. wuellerstorfi and bottom water d13CDIC, and on the other hand document severe depletions of taxonomically close relatives such as L. lobatula and C. pachyderma. At one station close to Bouvet Island at the western rim of Agulhas Basin, we interpret the offset of -1.5 per mil between bottom water d13CDIC and d13C values of infaunal living Bulimina aculeata in contrast to about -0.6 +/- 0.1 per mil measured at eight stations close-by, as a direct reflection of locally increased organic matter fluxes and sedimentation rates. Alternatively, we speculate that methane locally released from gas vents and related to hydrothermal venting at the mid-ocean ridge might have caused this strong depletion of 13C in the benthic foraminiferal carbon isotopic composition. Along the African continental margin, offsets between deep infaunal Globobulimina affinis and epibenthic Fontbotia wuellerstorfi as well as between shallow infaunal Uvigerina peregrina and F. wuellerstorfi, d13C values tend to increase with generally increasing organic matter decomposition rates. Although clearly more data are needed, these offsets between species might be used for quantification of biogeochemical paleogradients within the sediment and thus paleocarbon flux estimates. Furthermore, our data suggest that in high-productivity areas where sedimentary carbonate contents are lower than 15 weight %, epibenthic and endobenthic foraminiferal d13C values are strongly influenced by 13C enrichment probably due to carbonate-ion undersaturation, whereas above this sedimentary carbonate threshold endobenthic d13C values reflect depleted pore water d13CDIC values.

Percentages of sand-sized material and biogenic components in sediment core GIK12392-1

The paleo-oceanography of the southeastern North Atlantic Ocean during the last 150,000 yr has been studied using biogenous and terrigenous components of hemipelagic sediments sampled close to the northwest African continental margin. Variations of oxygen isotope ratios in shells of benthic calcareous foraminifers in two cores allow the assignment of absolute ages to these cores (in the best case at 1000 yr increments). The uncorrected bulk sedimentation rates of the longest core range from 3.4 to 7.6 cm/ 1000 yr during Interglacial conditions, and from 6.5 to 9.9 cm/1000 yr during Glacial conditions; all other cores have given results of the same order of magnitude, but with generally increasing values towards the continental edge. The distribution of sediment components allow us to make inferences about paleo-oceanographic changes in this region. Frequencies of biogenic components from benthic organisms, oxygen isotope ratios measured in benthic calcareous foraminiferal shells, the total carbonate contents of the sediment and distributions of biogenic components from planktonic organisms often fluctuate in concert. However, all fluctuations which can be attributed to changes of the bottom water masses (North Atlantic Deep Water) seem to precede by several thousand years those which can be linked to changes of the surface water mass distributions or to changes of the climate over the neighboring land masses. Late Quaternary planktonic foraminiferal assemblages in the cores from the northwest African continental margin can be defined satisfactorily in the way that distributions of assemblages found in sediment surface samples from the northeast Atlantic Ocean have been explained. The distributions of assemblages in the northwest African cores can also be used to estimate past sea surface temperatures and salinities. The downcore record of these estimates reveals two warm periods during the last 150,000 yr, the lower one corresponding to the oxygen isotope stage 5 e (equivalent to the Eemian proper in Europe), the upper one to the younger half of the Holocene. Winter surface water temperatures during oxygen isotope stages 6, 4, 3, and 2 are remarkably constant in most cores, while summer sea surface temperatures during stage 3 reach values comparable to those of the warm periods during the Late Holocene and Eemian. Estimated winter sea surface temperatures range from > 16 °C to < 11°C, the summer sea surface temperatures from > 22 °C to < 15 °C during the last 150,000 yr. Estimates of the winter sea surface salinities fluctuate between 36.6? and 35.5?, the higher values being restricted to the warm periods since the penultimate Glacial. Estimates for sea surface temperatures and salinities for two cores from the center of today's coastal upwelling region show less pronounced fluctuations than the record of the open ocean cores in the case of the station 12379 off Cape Barbas, more pronounced in the case of station 12328 off Cape Blanc. Seasonal differences between winter and summer sea surface temperatures derived from the estimated temperatures are today more pronounced in the boundary region of the ocean to the continent than further away from the continent. The differences are generally higher during warm climatic periods of the last 150,000 yr than during cooler ones. The abundance of terrigenous grains in the coarse fractions generally decreases with increasing distance from the continental edge, and also from south to north. The dominant portion of the terrigenous detritus is carried out into the ocean during the relatively cool climatic periods (stage 6, 4, later part of stage 3, stage 2 and oldest part of stage 1). The enhanced precision of dating combined with the stratigraphic resolution of these high deposition rate cores make it clear that the peaks of the terrigenous input off this part of the northwest African continental margin occur simultaneously with times of rapid sea level fluctuations resulting from large volume changes of the large Glacial ice sheets.

(Table 1) Age determination of Chukchi Sea sediments

Dinocysts from cores collected in the Chukchi Sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques. Holocene sequences have been recovered in a down-slope core (B15: 2135 m, 75°44'N, sedimentation rate of ~1 cm/kyr) and in a shelf core (P1: 201 m, 73°41'N, sedimentation rate of ~22 cm/kyr). The shelf record spanning about 8000 years suggests high-frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar (cal) years B.P. The condensed offshore record (B15) reveals an early postglacial optimum with minimum sea ice cover prior to 12,000 cal years B.P., which corresponds to a terrestrial climate optimum in Bering Sea area. Dinocyst data indicate extensive sea ice cover (>10 months/yr) from 12,000 to 6000 cal years B.P. followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions, superimposed on large-amplitude millennial-scale oscillations. In contrast, d18O data in mesopelagic foraminifers (Neogloboquadrina pachyderma) and benthic foraminifers (Cibicides wuellerstorfi) reveal maximum subsurface temperature and thus maximum inflow of the North Atlantic water around 8000 cal years B.P., followed by a trend toward cooling of the subsurface to bottom water masses. Sea-surface to subsurface conditions estimated from dinocysts and d18O data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate North Atlantic water mass with the existence of a sharp halocline and a reverse thermocline, especially before 6000 years B.P. The overall data and sea ice reconstructions from core B15 are consistent with strong sea ice convergence in the western Arctic during the early Holocene as suggested on the basis of climate model experiments including sea ice dynamics, matching a higher inflow rate of North Atlantic Water.

Nd isotopes an geochemistry of bulk deep sea sediments of the Atlantic Ocean

Nd isotopes preserved in fossil fish teeth and ferromanganese crusts have become a common tool for tracking variations in water mass composition and circulation through time. Studies of Nd isotopes extracted from Pleistocene to Holocene bulk sediments using hydroxylamine hydrochloride (HH) solution yield high resolution records of Nd isotopes that can be interpreted in terms of deep water circulation, but concerns about diagenesis and potential contamination of the seawater signal limit application of this technique to geologically young samples. In this study we demonstrate that Nd extracted from the > 63 µm, decarbonated fraction of older Ocean Drilling Program (ODP) sediments using a 0.02 M HH solution produces Nd isotopic ratios that are within error of values from cleaned fossil fish teeth collected from the same samples, indicating that the HH-extractions are robust recorders of deep sea Nd isotopes. This excellent correlation was achieved for 94 paired fish teeth and HH-extraction samples ranging in age from the Miocene to Cretaceous, distributed throughout the north, tropical and south Atlantic, and composed of a range of lithologies including carbonate-rich oozes/chalks and black shales. The strong Nd signal recovered from Cretaceous anoxic black shale sequences is unlikely to be associated with ferromanganese oxide coatings, but may be derived from abundant phosphatic fish teeth and debris or organic matter in these samples. In contrast to the deep water Nd isotopic signal, Sr isotopes from HH-extractions are often offset from seawater values, suggesting that evaluation of Sr isotopes is a conservative test for the integrity of Nd isotopes in the HH fraction. However, rare earth elements (REE) from the HH-extractions and fish teeth produce distinctive middle REE bulge patterns that may prove useful for evaluating whether the Nd isotopic signal represents uncontaminated seawater. Alternatively, a few paired HH-extraction and cleaned fish teeth samples from each site of interest can be used to verify the seawater composition of the HH-extractions. The similarity between isotopic values for the HH-extraction and fish teeth illustrates that the extensive cleaning protocol applied to fish teeth samples is not necessary in typical, carbonate-rich, deep sea sediments.

Micropaleontological investigation of sediment core Kronsmoor

Benthic foraminiferal and calcareous nannofossil assemblages, as well as stable isotope data from the Campanian/Maastrichtian boundary interval (~71.4 to ~70.7 Ma) of the Kronsmoor section (North German Basin), were investigated in order to characterize changes in surface-water productivity and oxygen content at the seafloor and their link to climatic and paleoceanographic changes. A nutrient index based on calcareous nannofossils is derived for the high-latitude, epicontinental North German Basin, reflecting changes in surface-water productivity. Oxygen isotopes of well-preserved planktic foraminiferal specimens of Heterohelix globulosa reflect warmer surface-water temperatures in the lower part of the studied succession and a cooling of up to 2°C (0.5 per mil) in the upper part (after 71.1 Ma). For the lower and warmer part of the investigated succession, benthic foraminiferal assemblages and the calcareous nannofossils indicate well-oxygenated bottom waters and low-surface water productivity. In contrast, the upper part of the succession is characterized by cooler conditions, lower oxygen content at the seafloor and increasing surface-water productivity. It is proposed that the cooling phase starting at 71.1 Ma was accompanied by increasing surface-water mixing caused by westerly winds. As a consequence of mixing, nutrients were advected from sub-surface waters into the mixed layer, resulting in increased surface-water productivity and enhanced organic matter flux to the seafloor. We hypothesize that global sea-level fall during the earliest Maastrichtian (~71.3 Ma), indicated by decreasing carbon isotope values, may have led to a weaker water mass exchange through narrower gateways between the Boreal Realm and the open North Atlantic and Tethys oceans. Both the weaker water mass exchange and enhanced surface-water productivity may have led to slightly less ventilated bottom waters of the upper part of the studied section. Our micro-paleontological and stable isotopic approach indicates short-term (<100 kyr) changes in oxygen consumption at the seafloor and surface-water productivity across the homogeneous Boreal White Chalk succession of the North German Basin.

Stable carbon and oxygen isotope ratios of Planulina wuellerstorfi from sediments of the Vema Channel

Oxygen- and carbon-isotopic analyses have been performed on the benthic foraminifer Planulina wuellerstorfi in seven Late Quaternary cores from the Vema Channel-Rio Grande Rise region. The cores are distributed over the water-depth interval of 2340 to 3939 m, which includes the present transition from North Atlantic Deep Water (NADW) to Antarctic Bottom Water (AABW). The carbon-isotopic records in the cores vary as a function of water depth. The shallowest and deepest cores show no significant glacial-interglacial difference in delta13C. Four of the five cores presently located in the NADW have benthic foraminiferal delta13C that is lower during glacial isotopic stages. Based on bathymetric gradients in delta13C, we conclude that, like today, there were two water masses present in the Vema Channel during glacial intervals: a water mass enriched in 13C overlying another water mass depleted in 13C. The largest gradient of change of delta13C with depth, however, occurred at 2.7 km, ~1 km shallower than the present position of this gradient. On the basis of paleontologic and sedimentologic evidence, we consider it unlikely that the NADW:AABW transition shallowed to this level. Reduced carbon-isotopic gradients between the deep basins of the North Atlantic and Pacific Oceans during the last glaciation suggest that production of NADW was reduced. Lower production of NADW may have modified the local abyssal circulation pattern in the Vema Channel region.

Grain-size, lithic grains, foraminifera-derived and dinocyst-derived data of sediment core MD99-2281

The last glacial period was punctuated by abrupt climatic events with extrema known as Heinrich and Dansgaard-Oeschger events. These millennial events have been the subject of many paleoreconstructions and model experiments in the past decades, but yet the hydrological processes involved remain elusive. In the present work, high-resolution analyses were conducted on the 12-42 ka BP section of core MD99-2281 retrieved southwest of the Faeroe Islands, and combined with analyses conducted in two previous studies (Zumaque et al., 2012; Caulle et al., 2013). Such a multiproxy approach, coupling micropaleontological, geochemical and sedimentological analyses, allows us to track surface, subsurface, and deep hydrological processes occurring during these rapid climatic changes. Records indicate that the coldest episodes of the studied period (Greenland stadials and Heinrich stadials) were characterized by a strong stratification of surface waters. This surface stratification seems to have played a key role in the dynamics of subsurface and deep-water masses. Indeed, periods of high surface stratification are marked by a coupling of subsurface and deep circulations which sharply weaken at the beginning of stadials, while surface conditions progressively deteriorate throughout these cold episodes; conversely, periods of decreasing surface stratification (Greenland interstadials) are characterized by a coupling of surface and deep hydrological processes, with progressively milder surface conditions and gradual intensification of the deep circulation, while the vigor of the subsurface northward Atlantic flow remains constantly high. Our results also reveal different and atypical hydrological signatures during Heinrich stadials (HSs): while HS1 and HS4 exhibit a "usual" scheme with reduced overturning circulation, a relatively active North Atlantic circulation seems to have prevailed during HS2, and HS3 seems to have experienced a re-intensification of this circulation during the middle of the event. Our findings thus bring valuable information to better understand hydrological processes occurring in a key area during the abrupt climatic shifts of the last glacial period.

Stable isotope ratios of benthic foraminifera stable from Miocene Pacific sediments, DSDP Leg 29, Site 281 (Table 2)

Seven Miocene Pacific Ocean Deep Sea Drilling Project sites from four different water masses (planktonic foraminiferal biogeographic regions) have been correlated using 18 prominent carbon isotopic events defined in the benthic foraminiferal delta13C records in DSDP Site 289. The correlations are based on the assumption that there are global or at least Pacific-wide controls on the delta13C of deep-water [HCO3]**-. Each of the individual delta13C records is correlated to Site 289 based on the shape of the curves in a manner analogous to that used to correlate sea-floor magnetic anomaly patterns. The results of this correlation experiment confirm that planktonic foraminiferal biostratigraphy and carbon isotopic stratigraphy are consistent within the tropical surface water mass and precise to +/-100,000 years. Correlations between surface water masses suggest that the precision of foraminiferal biostratigraphy is on the average less than +/-200,000 years due to the lack of cosmopolitan marker species and diachronism of species occurrences. Carbon isotope stratigraphy used in conjunction with biostratigraphy has the potential to provide an easily utilized, globally applicable, correlation tool (with an interregional precision of +/-100,000 years or better) as more continuous and undisturbed deep-sea sections become available as a result of the Hydraulic Piston Coring Program.

Stable isotope ratios of benthic and planktonic foraminifera from Miocene to Pliocene sediments of DSDP Hole 7-62A on the Eauripik Rise, Pacific Ocean (Table 1)

Oxygen and carbon isotope analyses show that the biserial forarniniferal genus Streptochilus, which was originally described from pelagic sediments on the Eauripik Rise and Ontong Java Plateau, lived deep in the upper water column within the oxygen minimum layer. The species of Streptochilus average from 4 to 19% of the foraminiferal assemblages in which benthic forms compose less than 1 or 2%. Specimens of Streptochilus are selectively dissolved when in contact with the bottom water mass. Their rapid evolutionary turnover of less than a few million years and their wide areal distribution in the equatorial Indo-Pacific are indicative of planktonic foraminifera. Aside from usefulness of the species of Streptochilus as stratigraphic indices, these Neogene biserial planktonic foraminifera are potential indices of paleoceanographic stratification.