Eocene-Oligocene sea surface temperature and pCO2 estimates

The long-term cooling trend of the Cenozoic is punctuated by shorter-term climatic events, such as the inception of permanent ice sheets on Antarctica at the Eocene?Oligocene Transition (~33.7 Ma). Taking advantage of the excellent state of preservation of coccolith calcite in equatorial Atlantic deep-sea cores, we unveil progressive tropical warming in the Atlantic Ocean initiated 4 million years prior to Antarctic glaciation. Warming preceding glaciation may appear counterintuitive, but we argue that this long-term climatic precursor to the EOT reinforced cooling of austral high latitudes via the redistribution of heat at the surface of the oceans. We discuss this new prominent paleoceanographic and climatic feature in the context of overarching pCO2 decline and the establishment of an Antarctic circumpolar current.

Meiofauna of surface sediments in the Cretan Sea

Quantitative information on metazoan meiofaunal abundance and biomass was obtained from three continental shelf (at 40, 100 and 200 m depth) and four deep-sea stations (at 540, 700, 940 and 1540 m depth) in the Cretan Sea (South Aegean Sea, NE Mediterranean). Samples were collected on a seasonal basis (from August 1994 to September 1995) with the use of a multiple corer. Meiofaunal abundance and biomass on the continental shelf of the Cretan Sea were high, in contrast to the extremely low values reported for the bathyal sediments that showed values comparable to those reported for abyssal and hadal environments. In order to explain the spatial and seasonal changes in metazoan meiofauna these data were compared with: (1) the concentrations of 'food indicators' (such as proteins, lipids, soluble carbohydrates and CPE) (2) the bacterial biomass (3) the flux of labile organic compounds to the sea floor at a fixed station (D7, 1540 m depth). Highly significant relationships between meiofaunal parameters and CPE, protein and lipid concentrations and bacterial biomass were found. Most of the indicators of food quality and quantity (such as CPE, proteins and carbohydrates) showed a clear seasonality with highest values in February and lowest in September. Such changes were more evident on the continental shelf rather than at deeper depths. On the continental shelf, significant seasonal changes in meiofaunal density were related to changes in the input of labile organic carbon whereas meiofaunal assemblages on the deep-sea stations showed time-lagged changes in response to the food input recorded in February 95. At all deep-sea stations meiofaunal density increased with a time lag of 2 months. Indications for a time-lagged meiofaunal response to the food inputs were also provided by the increase in nauplii densities during May 95 and the increase in individual biomass of nematodes, copepods and polychaetes between February and May 1995. The lack of strong seasonal changes in deep sea meiofaunal density suggests that the supply of organic matter below 500 m is not strong enough to support a significant meiofaunal development. Below 700 m depth >92% of the total biomass in the sediment was represented by bacteria. The ratio of bacterial to meiofaunal biomass increased with increasing water depth indicating that bacteria are probably more effective than meiofauna in exploiting refractory organic compounds. These data lead us to hypothesise that the deep-sea sediments of the Cretan Sea are largely dependent upon a benthic microbial loop.

Chemical composition of tephra from the Greenland-Iceland-Norwegian-Sea

Explosive ocean island volcanism in the Greenland-Iceland-Norwegian Sea (GIN Sea) is indicated by marine tephra layers at 10-300 ka. Peaks of explosive volcanism occurred in oxygen isotope stages 8, 7, 5 and 1. The depositional age of the tephra was estimated using the oxygen isotope stratigraphy and dating of marine records. Geochemical analyses of the tephra layers show that all originate from Iceland. Here we report the characteristics of tephra from these major Icelandic events in 30 deep-sea cores from the GIN Sea. Our findings provide constraints on the distribution of tephra from the eruption source. For the Vedde Ash (oxygen isotope stage 1) we estimate a minimum fallout area of 2*10**5 km**2, stretching from central Greenland in the west and southern Sweden in the east, to 71°N in the GIN Sea. The magnitude of the eruption and the regional wind conditions controlled the extent and concentrations of these ash fallout events. Oceanic circulation and differential settling may have affected the distribution and final deposition of ash particles such as bubble wall shards.

Seafloor spreading magnetic anomaly isochron map compilation for the Weddell Sea and Scotia Sea

The deep sea sedimentary record is an archive of the pre-glacial to glacial development of Antarctica and changes in climate, tectonics and ocean circulation. Identification of the pre-glacial, transitional and full glacial components in the sedimentary record is necessary for ice sheet reconstruction and to build circum-Antarctic sediment thickness grids for past topography and bathymetry reconstructions, which constrain paleoclimate models. A ~3300 km long Weddell Sea to Scotia Sea transect consisting of multichannel seismic reflection data from various organisations, were used to interpret new horizons to define the initial basin-wide seismostratigraphy and to identify the pre-glacial to glacial components. We mapped seven main units of which three are in the inferred Cretaceous-Paleocene pre-glacial regime, one in the Eocene-Oligocene transitional regime and three units in the Miocene-Pleistocene full glacial climate regime. Sparse borehole data from ODP leg 113 and SHALDRIL constrain the ages of the upper three units. Compiled seafloor spreading magnetic anomalies constrain the basement ages and the hypothetical age model. In many cases, the new horizons and stratigraphy contradict the interpretations in local studies. Each seismic sedimentary unit and its associated base horizon are continuous and traceable for the entire transect length, but reflect a lateral change in age whilst representing the same deposition process. The up to 1240 m thick pre-glacial seismic units form a mound in the central Weddell Sea basin and, in conjunction with the eroded flank geometry, support the interpretation of a Cretaceous proto-Weddell Gyre. The base reflector of the transitional seismic unit, which marks the initial ice sheet advances to the outer shelf, has a lateral model age of 26.6-15.5 Ma from southeast to northwest. The Pliocene-Pleistocene glacial deposits reveals lower sedimentations rates, indicating a reduced sediment supply. Sedimentation rates for the pre-glacial, transitional and full glacial components are highest around the Antarctic Peninsula, indicating higher erosion and sediment supply of a younger basement. We interpret an Eocene East Antarctic Ice Sheet expansion, Oligocene grounding of the West Antarctic Ice Sheet and Early Miocene grounding of the Antarctic Peninsula Ice Sheet.

(Table T1) Initial water quality conditions for bioassay experiments during Nathaniel B. Palmer cruise NBP09-01 in the Amundsen Sea

Nutrient addition experiments were performed during the austral summer in the Amundsen Sea (Southern Ocean) to investigate the availability of organically bound iron (Fe) to the phytoplankton communities, as well as assess their response to Fe amendment. Changes in autotrophic biomass, pigment concentration, maximum photochemical efficiency of photosystem II, and nutrient concentration were recorded in response to the addition of dissolved free Fe (DFe) and Fe bound to different model ligands. Analysis of pigment concentrations indicated that the autotrophic community was dominated by the prymnesiophyte Phaeocystis antarctica throughout most of the Amundsen Sea, although diatoms dominated in two experiments conducted in the marginal ice zone. Few significant differences in bulk community biomass (particulate organic carbon, nitrogen, and chlorophyll a) were observed, relative to the controls, in treatments with Fe added alone or bound to the ligand phytic acid. In contrast, when Fe was bound to the ligand desferrioxamine B (DFB), decreases in the bulk biomass indices were observed. The concentration of the diatom accessory pigment fucoxanthin showed little response to Fe additions, while the concentration of the P. antarctica-specific pigment, 19'-hexanoyloxyfucoxanthin (19'-hex), decreased when Fe was added alone or bound to the model ligands. Lastly, differences in the nitrate:phosphate (NO3- :PO4**3-) utilization ratio were observed between the Fe-amended treatments, with Fe bound to DFB resulting in the lowest NO3- :PO4**3- uptake ratios (~ 10) and the remaining Fe treatments having higher NO3- :PO4**3- uptake ratios (~ 17). The data are discussed with respect to glacial inputs of Fe in the Amundsen Sea and the bioavailability of Fe. We suggest that the previously observed high NO3- :PO4**3- utilization ratio of P. antarctica is a consequence of its production of dissolved organic matter that acts as ligands and increases the bioavailability of Fe, thereby stimulating the uptake of NO3-.

Sea surface temperature reconstruction for the middle Pleistocene from sediment core MD03-2699

Past sea surface water conditions of the western Iberian Margin were reconstructed based on biomarker analyses of a marine deep sea core MD03-2699 from the Estremadura Spur north off Lisbon, providing new insights into orbital and suborbital-scale climate variability between marine isotope stage (MIS) 15 to MIS 9 (580 to 300 ka). We use biomarker-based proxy records such as the alkenone unsaturated index to estimate sea surface temperature (SST), the total alkenone concentration to reconstruct phytoplankton productivity, and terrestrial biomarkers to evaluate the continental input. The results extend the existing biomarker record, namely the SST for the Iberian Margin, back to the sixth climatic cycle (580 ka). A general trend of stable interglacials contrasts with glacial periods and glacial inceptions which are marked by high-frequency variability. Thus, several short-lived climatic coolings were identified by large SST decreases, the occurrence of ice-rafted detritus and high percentages of the tetraunsaturated alkenone C 37:4. Some of these events were extremely cold and similar in their general trends to the well-known Heinrich events of the last glaciation. We identified eight Heinrich-type events between 580 and 300 ka. The general deglaciation pattern detected between MIS 15 and MIS 9 is similar in their general trends to that characterizing the more recent climatic cycles, i.e., marked by two coolings separated by a short warming episode which may reflect the southward, northward, and southward migration of the Polar Front.

Sea-bed photographs (benthos) from the AWI-Hausgarten area along OFOS profile PS62/191-1

Although the use of deep-sea imagery considerably increased during the last decades, reports on nekton falls to the deep seafloor are very scarce. Whereas there are a few reports describing the finding of whale carcasses in the deep north-eastern and south-eastern Pacific, descriptions of invertebrate or vertebrate food-falls at centimetre to metre scale are extremely rare. After 4 years of extensive work at a deep-sea long-term station in northern polar regions (AWI-"Hausgarten"), including large-scale visual observations with various camera systems covering some 10 000 m2 of seafloor at water depths between 1250 and 5600 m, this paper describes the first observation of a fish carcass at about 1280 m water depth, west off Svålbard. The fish skeleton had a total length of 36 cm and an approximated biomass of 0.5 kg wet weight. On the basis of in situ experiments, we estimated a very short residence time of this particular carcass of about 7 h at the bottom. The fast response of the motile deep-sea scavenger community to such events and the rapid utilisation of this kind of organic carbon supply might partly explain the extreme rarity of such an observation.

Sea surface temperatures reconstructed from alkenones of surface sediment samples of the Argentine Basin at stations GeoB1501-1 to GeoB2830-1

We analysed the alkenone unsaturation ratio (UK'37) in 87 surface sediment samples from the western South Atlantic (5°N-50°S) in order to evaluate its applicability as a paleotemperature tool for this part of the ocean. The measured UK'37 ratios were converted into temperature using the global core-top calibration of Müller et al. (1998, doi:10.1016/S0016-7037(98)00097-0) and compared with annual mean atlas sea-surface temperatures (SSTs) of overlying surface waters. The results reveal a close correspondence (<1.5°C) between atlas and alkenone temperatures for the Western Tropical Atlantic and the Brazil Current region north of 32°S, but deviating low alkenone temperatures by -2° to -6°C are found in the regions of the Brazil-Malvinas Confluence (35-39°S) and the Malvinas Current (41-48°S). From the oceanographic evidence these low UK'37 values cannot be explained by preferential alkenone production below the mixed layer or during the cold season. Higher nutrient availability and algal growth rates are also unlikely causes. Instead, our results imply that lateral displacement of suspended particles and sediments, caused by strong surface and bottom currents, benthic storms, and downslope processes is responsible for the deviating UK'37 temperatures. In this way, particles and sediments carrying a cold water UK'37 signal of coastal or southern origin are transported northward and offshore into areas with warmer surface waters. In the northern Argentine Basin the depth between displaced and unaffected sediments appears to coincide with the boundary between the northward flowing Lower Circumpolar Deep Water (LCDW) and the southward flowing North Atlantic Deep Water (NADW) at about 4000 m.

Raw data of SCADCP (self-contained Acoustic Doppler Current Profiler) from three moorings in the Eastern Weddell Sea in 2005

Ten-month time series of mean volume backscattering strength (MVBS) and vertical velocity obtained from three moored acoustic Doppler current profilers (ADCPs) deployed from February until December 2005 at 64°S, 66.5°S and 69°S along the Greenwich Meridian were used to analyse the diel vertical zooplankton migration (DVM) and its seasonality and regional variability in the Lazarev Sea. The estimated MVBS exhibited distinct patterns of DVM at all three mooring sites. Between February and October, the timing of the DVM and the residence time of zooplankton at depth were clearly governed by the day-night rhythm. Mean daily cycles of the ADCP-derived vertical velocity were calculated for successive months and showed maximum ascent and descent velocities of 16 and -15 mm/s. However, a change of the MVBS pattern occurred in late spring/early austral summer (October/November), when the zooplankton communities ceased their synchronous vertical migration at all three mooring sites. Elevated MVBS values were then concentrated in the uppermost layers (<50 m) at 66.5°S. This period coincided with the decay of sea ice coverage at 64°S and 66.5°S between early November and mid-December. Elevated chlorophyll concentrations, which were measured at the end of the deployment, extended from 67°S to 65°S and indicated a phytoplankton bloom in the upper 50 m. Thus, we propose that the increased food supply associated with an ice edge bloom caused the zooplankton communities to cease their DVM in favour of feeding.

Stable isotope record, calcium carbonate conentrations, and sea surface temperture reconstructions of sediment cores from the North Atlantic

We analyze five high-resolution time series spanning the last 1.65 m.y.: benthic foraminiferal delta18O and delta13O, percent CaCO3, and estimated sea surface temperature (SST) at North Atlantic Deep Sea Drilling Project site 607 and percent CaCO3 at site 609. Each record is a multicore composite verified for continuity by splicing among multiple holes. These climatic indices portray changes in northern hemisphere ice sheet size and in North Atlantic surface and deep circulation. By tuning obliquity and precession components in the delta18O record to orbital variations, we have devised a time scale (TP607) for the entire Pleistocene that agrees in age with all K/Ar-dated magnetic reversals to within 1.5%. The Brunhes time scale is taken from Imbrie et al. [1984], except for differences near the stage 17/16 transition (0.70 to 0.64 Ma). All indicators show a similar evolution from the Matuyama to the Brunhes chrons: orbital eccentricity and precession responses increased in amplitude; those at orbital obliquity decreased. The change in dominance from obliquity to eccentricity occurred over several hundred thousand years, with fastest changes around 0.7 to 0.6 Ma. The coherent, in-phase responses of delta18O, delta13O, CaCO3 and SST at these rhythms indicate that northern hemisphere ice volume changes have controlled most of the North Atlantic surface-ocean and deep-ocean responses for the last 1.6 m.y. The delta13O, percent CaCO3, and SST records at site 607 also show prominent changes at low frequencies, including a prominent long-wavelength oscillation toward glacial conditions that is centered between 0.9 and 0.6 Ma. These changes appear to be associated neither with orbital forcing nor with changes in ice volume.