Description: Highlights • Planktic foraminifera species show an Early Holocene 14C plateau analogous to the atmospheric 14C plateau at 10.2–9.6 cal ka. • Age-calibrated Early Holocene 14C plateau boundaries provide precise age control in 3 sediment cores on a 900 km long transect. • Differences between planktic foraminiferal and atmospheric 14C ages reveal the 14C reservoir age of local surface waters. • Different planktic species document different 14C reservoir ages characteristic of different surface and subsurface waters. To trace spatial variations in Holocene reservoir ages of surface and subsurface waters we studied narrowly spaced 14C records of planktic foraminifera in three high-sedimentation rate cores from the Nordic Seas, the Barents Sea continental margin and eastern Fram Strait. The two northern cores reveal a distinct Early Holocene 14C plateau in dates on the subsurface dweller Neogloboquadrina pachyderma at 9.3–9.1 14C ka. The plateau was tuned to an atmospheric 14C plateau at 9.0–8.7 14C ka that spans 10.2–9.6 calendar ka. These two plateau boundaries provide robust age control points to estimate short-term changes in sedimentation rate and to correlate paleoceanographic signals over 900 km along the West Spitsbergen Current. The difference between planktic and atmospheric 14C plateau ages suggests local 14C reservoir ages of 370–400 yr. Planktic foraminifera species that inhabit different water masses document different reservoir ages. By comparison, the subpolar N. incompta reveals a reservoir age of 150 yr, probably formed in well-mixed Atlantic-sourced waters during winter. The near-surface dweller Turborotalita quinqueloba shows an age of 290 yr in the Fram Strait, but one of 720 yr at the Barents Sea continental margin. The latter age suggests a calcification within old, meltwater-enriched Arctic surface waters admixed by the East Spitsbergen Current. Likewise, we assign an elevated reservoir age of 760 yr on mixed species at a Norwegian Sea site near 71°N to Preboreal meltwaters that spread from northern Norway far west, also documented by the spatial distribution of a coeval δ13C minimum of N. pachyderma.

Description: The last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric CO2 and 14C. We employed the “14C plateau-tuning technique” to a centennial-scale planktic 14C record of core MD08-3180 retrieved S.W. of the Azores Islands at ∼3060 m water depth to establish both a new standard of absolute age control and a record of past 14C reservoir ages of ocean surface waters. Both δ18O minima of G. bulloides and high planktic reservoir ages of ∼1600 to 2170 yr suggest two major melt water incursions that reached from the Labrador Sea up to the subtropics over Heinrich Stadial 1 (HS-1). In parallel, we established a record of (apparent) benthic ventilation ages that add the planktic 14C reservoir ages together with the benthic-planktic 14C age difference at the site and time of deposition, a sum finally adjusted to past changes in atmospheric 14C that occurred since the time of deep-water formation. Near the Azores apparent deep-water ages of the Last Glacial Maximum were as low as 340–740 yr, which suggests a lateral advection of young North Atlantic Deep Waters (NADW) from subpolar regions south of Iceland, in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep-water formation. During HS-1, local benthic ventilation ages increased up to 2200–2550 yr, thus suggest an incursion of old southern-source deep waters, an unstable regime that was interrupted by brief pulses of NADW incursion near 16, 15.6 cal. ka, and most salient, near 14.9/14.7 ka.

Description: The ultimate, possibly geodynamic control and potential impact of changes in circulation activity and salt discharge of Mediterranean outflow waters (MOW) on Atlantic meridional overturning circulation have formed long-standing objectives in paleoceanography. Late Pliocene changes in the distal advection of MOW were reconstructed on orbital timescales for northeast Atlantic DSDP/ODP sites 548 and 982 off Brittany and on Rockall Plateau, supplemented by a proximal record from Site U1389 west off Gibraltar, and compared to Western Mediterranean surface and deep-water records of Alboran Sea Site 978. From ~3.43 to 3.3 Ma, MOW temperatures and salinities form a prominent rise by 2–4 °C and ~3 psu, induced by a preceding and coeval rise in sea surface and deep-water salinity and increased summer aridity in the Mediterranean Sea. We speculate that these changes triggered an increased MOW flow and were ultimately induced by a persistent 2.5 °C cooling of Indonesian Through-Flow waters. The temperature drop resulted from the northward drift of Australia that crossed a threshold value near 3.6–3.3 Ma and led to a large-scale cooling of the eastern subtropical Indian Ocean and in turn, to a reduction of African monsoon rains. Vice versa, we show that the distinct rise in Mediterranean salt export after ~3.4 Ma induced a unique long-term rise in the formation of Upper North Atlantic Deep Water, that followed with a phase lag of ~100 ky. In summary, we present evidence for an interhemispheric teleconnection of processes in the Indonesian Gateways, the Mediterranean and Labrador Seas, jointly affecting Pliocene climate.

Description: Ice core records demonstrate a glacial–interglacial atmospheric CO2 increase of ~ 100 ppm, while 14C calibration efforts document a strong decrease in atmospheric 14C concentration during this period. A calculated transfer of ~ 530 Gt of 14C-depleted carbon is required to produce the deglacial coeval rise of carbon in the atmosphere and terrestrial biosphere. This amount is usually ascribed to oceanic carbon release, although the actual mechanisms remained elusive, since an adequately old and carbon-enriched deep-ocean reservoir seemed unlikely. Here we present a new, though still fragmentary, ocean-wide Δ14C data set showing that during the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS-1) the maximum 14C age difference between ocean deep waters and the atmosphere exceeded the modern values by up to 1500 14C yr, in the extreme reaching 5100 14C yr. Below 2000 m depth the 14C ventilation age of modern ocean waters is directly linked to the concentration of dissolved inorganic carbon (DIC). We propose as a working hypothesis that the modern regression of DIC vs. Δ14C also applies for LGM times, which implies that a mean LGM aging of ~ 600 14C yr corresponded to a global rise of ~ 85–115 μmol DIC kg−1 in the deep ocean. Thus, the prolonged residence time of ocean deep waters may indeed have made it possible to absorb an additional ~ 730–980 Gt DIC, one third of which possibly originated from intermediate waters. We also infer that LGM deep-water O2 dropped to suboxic values of 〈 10 μmol kg−1 in the Atlantic sector of the Southern Ocean, possibly also in the subpolar North Pacific. The deglacial transfer of the extra-aged, deep-ocean carbon to the atmosphere via the dynamic ocean–atmosphere carbon exchange would be sufficient to account for two trends observed, (1) for the increase in atmospheric CO2 and (2) for the 190‰ drop in atmospheric Δ14C during the so-called HS-1 "Mystery Interval", when atmospheric 14C production rates were largely constant

Description: Near-surface sediments from the equatorial east Atlantic and the Norwegian Sea exhibit pronounced shear strength maxima in profiles from the peak Holocene and Pleistocene. These semi-indurated layers start to occur at 8–102 cm below the sediment surface and can be explained neither by the modal composition nor by the effective overburden pressure of the sediments. However, scanning electron microscope and microprobe data exhibit micritic crusts and crystal carpets, which are clearly restricted to (undisturbed) samples from indurated layers and form a manifest explanation for their origin. The minerals precipitated comprise calcite, aragonite, and in samples more proximal to the African continent SiO2 needles, and needles of as yet unidentified K-Mg-Fe-Al silicates, crusts of which dominate the indurated layers in the Norwegian Sea. By their stratigraphic position in deep-sea sediments the carbonate-based shear strength maxima are tentatively ascribed to dissolved adjacent pteropod layers from the early Holocene and hence to short-lived no-analogue events of early diagenesis. Possibly, they have been controlled by a reduced organic carbon flux, leading to increased aragonite preservation in the deep sea.

Description: A suit of sediment cores close to and south of the Strait of Gibraltar (12°-36°N, 500–2800 m water depth) were analyzed for stable isotopes in epibenthic foraminifers Cibicidoides wuellerstorfi and Planulina ariminensis. During peak glacial times, the data exhibit higher δ13C values of up to 1.6‰ at intermediate depths near the Strait of Gibraltar (36°N). The values decrease to the south as evidenced by our data, but also to the north as revealed by data of intermediate depth cores north of 38°N (in Duplessy et al. [1987]). Thus, the distribution pattern of δ13C provides crucial evidence for an increased influence of nutrient depleted Mediterranean Outflow Water (MOW) on the glacial northeast Atlantic hydrography. During oxygen isotope Terminations I and II, the meridional carbon isotope gradient indicates a significantly decreased but still active MOW. As deduced from the δ18O fluctuations, the temperatures of the MOW in the Atlantic were lower during glacial times by as much as 5°C. During glacial times and during Termination I the maximum δ13C values of the MOW correlate with minimum values of the North Atlantic Deep Water (NADW) and vice versa. This inverse response to climatic change of the carbon isotope signals of both water masses indicates, that the supply of saline MOW to the north Atlantic may be less important for the formation of NADW than previously assumed.

Description: Paleoceanographic and stratigraphic methods, based on high-resolution compressional wave (p-wave) velocity measurements, have been applied to the studies of late Quaternary deep-sea carbonates in the western and eastern equatorial Atlantic. The measurements provide sonostratigraphic records in which changes in p-wave velocity parallel the changes from a glacial to an interglacial climate: Maxima in p-wave velocity (greater than 1540 m/s) occur during interglacial oxygen isotope stages 1, 5 and 7. Minima (1490 m/s) occur during glacial oxygen isotope stages 2, 4 and 6. Changes in p-wave velocity parallel past changes in carbonate accumulation and sediment coarse fraction, and allow a detailed core to core correlation. From these results two main patterns emerge: (1) In cores from shallower than 4300 m and from well above the present lysocline, large temporal changes in p-wave velocity parallel the production of planktonic foraminifera and the climatic history recorded in the sediments, and (2) below 4300 m, the position of the foraminiferal lysocline in the western equatorial Atlantic, large downcore p-wave velocity fluctuations gradually disappear due to dissolution of carbonate sediments. Dissolution also causes a distinct decrease in p-wave velocity and acoustic reflectivity in surface sediments across the present foraminiferal lysocline. Thus, past changes in the position of the foraminiferal lysocline or calcite compensation depth that caused distinct changes in reflectivity of sediments should lead to distinct reflectors within sediment columns. Their distribution can be utilized to map paleowater masses with different degrees of carbonate saturation.

Description: Ocean Drilling Program (ODP) Site 982 provided a key sediment section at Rockall Plateau for reconstructing northeast Atlantic paleoceanography and monitoring benthic δ18O stratigraphy over the late Pliocene to Quaternary onset of major Northern Hemisphere glaciation. A renewed hole-specific inspection of magnetostratigraphic reversals and the addition of epibenthic δ18O records for short Pliocene sections in holes 982A, B, and C, crossing core breaks in the δ18O record published for Hole 982B, now imply a major revision of composite core depths. After tuning to the orbitally tuned reference record LR04, the new composite δ18O record results in a hiatus, where the Kaena magnetic subchron might have been lost, and in a significant age reduction for all proxy records by 130 to 20 ky over the time span 3.2–2.7 million years ago (Ma). Our study demonstrates the general significance of reliable composite-depth scales and δ18O stratigraphies in ODP sediment records for generating ocean-wide correlations in paleoceanography. The new concept of age control makes the late Pliocene trends in SST (sea surface temperature) and atmospheric pCO2 at Site 982 more consistent with various paleoclimate trends published from elsewhere in the North Atlantic.

Description: Eight time slices of surface-water paleoceanography were reconstructed from stable isotope and paleotemperature data to evaluate late Quaternary changes in density, current directions, and sea-ice cover in the Nordic Seas and NE Atlantic. We used isotopic records from 110 deep-sea cores, 20 of which are accelerator mass spectrometry (AMS)-14C dated and 30 of which have high (〉8 cm /kyr) sedimentation rates, enabling a resolution of about 120 years. Paleotemperature estimates are based on species counts of planktonic foraminifera in 18 cores. The δ18O and δ13C distributions depict three main modes of surface circulation: (1) The Holocene-style interglacial mode which largely persisted over the last 12.8 14C ka, and probably during large parts of stage 3. (2) The peak glacial mode showing a cyclonic gyre in the, at least, seasonally ice-free Nordic Seas and a meltwater lens west of Ireland. Based on geostrophic forcing, it possibly turned clockwise, blocked the S-N flow across the eastern Iceland-Shetland ridge, and enhanced the Irminger current around west Iceland. It remains unclear whether surface-water density was sufficient for deepwater formation west of Norway. (3) A meltwater regime culminating during early glacial Termination I, when a great meltwater lens off northern Norway probably induced a clockwise circulation reaching south up to Faeroe, the northward inflow of Irminger Current water dominated the Icelandic Sea, and deepwater convection was stopped. In contrast to circulation modes two and three, the Holocene-style circulation mode appears most stable, even unaffected by major meltwater pools originating from the Scandinavian ice sheet, such as during δ18O event 3.1 and the Bölling. Meltwater phases markedly influenced the European continental climate by suppressing the “heat pump” of the Atlantic salinity conveyor belt. During the peak glacial, melting icebergs blocked the eastward advection of warm surface water toward Great Britain, thus accelerating buildup of the great European ice sheets; in the early deglacial, meltwater probably induced a southward flow of cold water along Norway, which led to the Oldest Dryas cold spell.

Description: Great Belt, Vejsnäs Rinne and Boknis Rinne form a major interconnected channel System of approximately 80 km length and 30 m depth on the Kiel Bay sea floor, which generally is only some 10 to 20 m deep. 1971 to 1973, 32 transects were sampled across the channel slopes using narrow Station distances and systematically adding data (T°, S°/oo) from 5 hydrographic cross sections over a one and a half year period. A quantitative, combined study of the molluscan fauna, dead shells and Sediments yielded the following results. 30 species of bivalves and 19 of gastropods were sampled as livingspecimens. According to their long life span, Cypritta islandica is dominant in the deep and the Astarte species on the upper part of the channel slope. Macoma baltica is dominantin a third, more shallow Zone, which is actually outside of the channels. Abra alba is the most persistent species of the channels being present in 86% of all samples. Except for Hydrobia, gastropods display low numbers of presence and abundance and are almost never dominant. The bottom level of the thermohaline pycnocline impinges on the channel slope as a rule between (15-)18 and 22 (-25) m depth. This boundary layer is clearly reflected by the fauna, i.e. by maximum numbers of species and species richness, of species presence and abundance, as well as of the biomass of total molluscs and of most of the single mollusc species. The faunal Optimum is explained by the favourable combination of a suite of factors, such as relatively stable temperatures and increased salinity, sufficient aeration, and a strong “rain” of larvae and nutrition where the upper water mass is barred by the pycnocline. Substrate conditions (± 50 % of Sediment 〈 63 p) might be favourable as well. The deeper water mass of the channel System is increasingly plumbed by the pycnocline and correspondingly poor in oxygen concentration towards the inner end of the bay. The oxygen deficiency more and more confines the Optimum beit of the molluscs from below, and causes a distinct elevation of the maximum numbers of species, species richness, species dominance and biomass from the entrance towards the inner part of the bay from 20-24 to 15 -20 m depth. Increasing distance from the bay ’s entrance , (the Great Belt) does not exert any other influence on the molluscan fauna. Averaging the whole transects, the mean numbers of species, species richness, species presence and biomass stay constant in line with constant T-S conditions. The molluscan Optimum belt is widened on the slope towards the deep and partly doubled at current and water exposed parts of the slope, where it also achieves its absolute maximum numbers. No molluscan species is bound to a specific type of Sediment, though eventually certain Sediments may be preferred. Mud forms an exception in showing a clear decrease of the number of specimens (by an overlap with the factor oxygen deficiency). Except for the well known general reduction of species in the Kiel Bay, the distribution pattern of temp erature and salinity exerts only minor influences on the fauna. The dead-shell species as semblage generally reflects the living one. On the whole, they correspond with their composition of species, the zonation of dominant species (middle, emergent Astarte beit) and the distribution and elevation pattern of the maxima of species, species richness and dead-shell quantities. A downslope transport of shells is inferred, among other things, from a stronger presence of (dead-shell) species in the deeper part of the channel. As measured by the lateral displacement of the mollusc maximum belts, the transport amounts 1 to 3 m in vertical distance, rarely up to 7 m at current exposed slopes. These numbers correspond to 30-75 m horizontal distance. Besides currents, extreme wave action is a possible cause. Current induced long-distance transport of dead shells generates increased numbers of species, species presence and dead-shell quantities at the channel bottom, especially behind narrow passes. Hotvever, taking into account the undisturbed distribution of dominant species, the quantity of reworked shells must be insignificant. First indications of the shell production can be derived from the living-dead ratio of shell samples — notwithstanding the varying amounts of carbonate dissolution. For instance, the production of Astarte species is some 13 times smaller than the one of Abra alba and 7 times smaller than that of Cyprina islandica. — A general strong change from living to dead-shell dominance occurs below the pycnocline at 20 to 24 m depth. In the case of a fossil analogue of a Baltic Sea channel, marked shell horizons with a broad species spectrum most probably correspond to a molluscan zone at the level of the mean pycnocline Position.