Figure 2. Downcore variations of total diatom concentration in core MD02-2529

The modern eastern equatorial Pacific (EEP) is a major natural source for atmospheric carbon dioxide and is thought to be connected to high-latitude ocean dynamics by oceanic teleconnections on glacial-interglacial timescales. A wealth of sedimentary records aiming at reconstructing last Quaternary changes in primary productivity and nutrient utilization have been devoted to understanding those linkages between the EEP and other distant oceanic areas. Most of these records are, however, clustered in the pelagic EEP cold tongue, with comparatively little attention devoted to coastal areas. Here we present downcore measurements of the composition and concentration of the diatom assemblage together with opal (biogenic silica) concentration at site MD02-2529 recovered in the coastal Panama Basin. Piston core MD02-2529, collected in an area affected by a multitude of processes, provides evidence for strong variations in diatom production at the millennial timescale during the last glacial cycle. The maxima in total diatom concentration occurred during the early marine isotopic stage (MIS) 4 as well as during the MIS 4/3 transition and MIS 3. Rapid changes in diatom concentrations during the MIS 3 mimics Bond cycles as independently recorded by the SSS estimation derived from planktonic foraminifera from the same core. Such patterns indicate a clear linkage between diatom production in the coastal EEP and rapid climate changes in the high-latitude North Atlantic. In parallel, the long-term succession of the diatom community from coastal diatoms, predominantly thriving during MIS 5 and 4, towards pelagic diatoms, dominant during MIS 3 and 2, points to a long-term change in the surface hydrology. During Heinrich Events, diatoms strongly reduced their production, probably due to enhanced stratification in the upper water column. After the last glacial maximum, diatom production and valve preservation strongly decreased in response to the advection of nutrient (H2SiO4)-depleted, warmer water masses. Our high-resolution record highlights how regional climatic processes can modulate rapid changes in siliceous primary production as triggered by wind-induced local upwelling, indicating that millennial climatic variability can overtake other prominent hydrological processes such as those related to silicic acid leakage.

(Table T1) Depths and ages of datum levels at ODP Leg 182 sites

The first and last appearances of Quaternary planktonic foraminifers in the Great Australian Bight were evaluated using datum levels from magnetostatigraphy, oxygen isotope stratigraphy, and calcareous nannofossil biostratigraphy to determine whether they were synchronous or diachronous with open-ocean biostratigraphic events. The first appearance of Globorotalia truncatulinoides is diachronous at 1.6-1.7 Ma at Site 1127 and 1.1-1.2 at Sites 1129 and 1132, similar to other local appearances in high latitudes. All other datum levels, however, are synchronous with open-ocean events, including the first appearance of Globorotalia hirsuta and the last appearances of Globorotalia tosaensis and pink Globigerinoides ruber in the Indo-Pacific region. A local reappearance of Gt. hirsuta at ~0.12 Ma and the disappearance of Globorotalia crassaformis at ~0.10 Ma were found to be useful for local biostratigraphy. Age control at the bottom of all of the sections is poor at this time, but results suggest that sedimentation recommenced starting at ~1.9 Ma above the regional unconformity that marks the base of seismostratigraphic Sequence 2. Sediment accumulation is distinctly reduced in the lower Pleistocene compared to the upper Pleistocene, perhaps in part because of processes associated with several omission surfaces.

Sedimentology of cores from the shelf of Lazarev Sea, East Antarctica

Distinct facies types, classified in radiocarbon-dated sediments from the shelf of the Lazarev Sea, East Antarctica, reveal a detailed history of processes that have controlled sedimentation during the deglaciation over the last 10,000 yr. The ice retreat on this part of the Antarctic shelf started 9500 yr BP, marked by the deposition of laminated sediments, deposited from a floating ice shelf. These laminites, which occur on top of diamictons laid down from a grounded ice sheet, are the basal sediments of the postglacial sequence. The intensity of the Antarctic Coastal Current (ACC), directed by shelf morphology, controlled sedimentation of the postglacial facies. A residual glaciomarine sediment with the fine fraction winnowed by strong currents developed from 9000-8000 yr BP in the western part of the investigation area and from 9000-5000 yr BP in the eastern part, closer to the prominent 'Fenno Deep' trough. Current velocities apparently decreased between 8000 and 2000 yr BP due to a deflection of the ACC by advancing ice tongues to the east of the investigation area during the 'Hypsithermal'. This led to a deposition of fine-grained sediments, and clay mineralogy suggests a continental source, possibly near the grounding line of the Nivl Ice Shelf, rather than a winnowing of sediments near the shelf break or advection from deeper water. Current velocities intensified after 2000 yr BP, removed fine material from these sediments and led to a relict sediment, consisting of coarse bryozoan and molluscan debris.

Dinocyst-derived sea-surface characteristics, palynomorph abundances, ice-rafted debris, and planktonic foraminifera abundances and d18O of the 35-41 ka BP interval of core MD99-2285

The last glacial millennial climatic events (i.e. Dansgaard-Oeschger and Heinrich events) constitute outstanding case studies of coupled atmosphere-ocean-cryosphere interactions. Here, we investigate the evolution of sea-surface and subsurface conditions, in terms of temperature, salinity and sea ice cover, at very high-resolution (mean resolution between 55 and 155 years depending on proxies) during the 35-41 ka cal BP interval covering three Dansgaard-Oeschger cycles and including Heinrich event 4, in a new unpublished marine record, i.e. the MD99-2285 core (62.69°N; -3.57s°E). We use a large panel of complementary tools, which notably includes dinocyst-derived sea-ice cover duration quantifications. The high temporal resolution and multiproxy approach of this work allows us to identify the sequence of processes and to assess ocean-cryosphere interactions occurring during these periodic ice-sheet collapse events. Our results evidence a paradoxical hydrological scheme where (i) Greenland interstadials are marked by a homogeneous and cold upper water column, with intensive winter sea ice formation and summer sea ice melting, and (ii) Greenland and Heinrich stadials are characterized by a very warm and low saline surface layer with iceberg calving and reduced sea ice formation, separated by a strong halocline from a less warm and saltier subsurface layer. Our work also suggests that this stadial surface/subsurface warming started before massive iceberg release, in relation with warm Atlantic water advection. These findings thus support the theory that upper ocean warming might have triggered European ice-sheet destabilization. Besides, previous paleoceanographic studies conducted along the Atlantic inflow pathways close to the edge of European ice-sheets suggest that such a feature might have occurred in this whole area. Nonetheless, additional high resolution paleoreconstructions are required to confirm such a regional scheme.

Seawater carbonate chemistry and biological processes during experiments with spider crab Hyas araneus, 2009

Future scenarios for the oceans project combined developments of CO2 accumulation and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of elevated CO2 concentrations on thermal tolerance of the cold-eurythermal spider crab Hyas araneus from the population around Helgoland. Here ambient temperatures characterize the southernmost distribution limit of this species. Animals were exposed to present day normocapnia (380 ppm CO2), CO2 levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO2 (PeO2) were measured during progressive short term cooling from 10 to 0°C and during warming from 10 to 25°C. An increase of PeO2 occurred during cooling, the highest values being reached at 0°C under all three CO2 levels. Heart rate increased during warming until a critical temperature (Tc) was reached. The putative Tc under normocapnia was presumably >25°C, from where it fell to 23.5°C under 710 ppm and then 21.1°C under 3000 ppm. At the same time, thermal sensitivity, as seen in the Q10 values of heart rate, rose with increasing CO2concentration in the warmth. Our results suggest a narrowing of the thermal window of Hyas araneus under moderate increases in CO2 levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance.

Sea surafe temperture calculation for the Arabian Sea

Sea surface temperature (SST) and seawater d18O (d18Ow) were reconstructed in a suite of sediment cores from throughout the Arabian Sea for four distinct time intervals (0 ka, 8 ka, 15 ka, and 20 ka) with the aim of understanding the history of the Indian Monsoon and the climate of the Arabian Sea region. This was accomplished through the use of paired Mg/Ca and d18O measurements of the planktonic foraminifer Globigerinoides ruber. By analyzing basin-wide changes and changes in cross-basinal gradients, we assess both monsoonal and regional-scale climate changes. SST was colder than present for the majority of sites within all three paleotime slices. Furthermore, both the Indian Monsoon and the regional Arabian Sea mean climate have varied substantially over the past 20 kyr. The 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2.5°-3.5°C attributable, in part, to the influences of glacial atmospheric CO2 concentrations and large continental ice sheets. The elimination of the cross-basinal SST gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength. Changes in d18Ow that are smaller than the d18O signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing. SSTs throughout the Arabian Sea were still cooler than present by an average of 1.4°C in the 8 ka time slice. These cool SSTs, along with lower d18Ow throughout the basin, are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation. The results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling.

Physical oceanography during five ECOMARGE cruises

The first experiment of the ECOMARGE programme (ECOsystèmes de MARGE continentale) was initiated in 1983-1984, in the Gulf of Lions (northwestern Mediterranean Sea). The objectives of the ECOMARGE-I experiment were: to quantify the transfer of particulate matter, in general, and of organic carbon, in particular, from its introduction to and formation in the waters of the continental shelf-to its consumption or sedimentation on the shelf or its transfer to the slope and deep sea; and to understand the processes involved in that transfer, consumption and sedimentation together with their variability in space and time. The results of that experiment, from 1983 to 1988, are presented in this Special Issue. The highlights of the results are summarised in this paper. These results indicate that, of the particles formed in the waters of the continental shelf and those introduced by rivers, some are deposited as sediments on the shelf. A portion is transported offshore, however, to the slope and deep sea. The Rho^ne River, in the northeastern part of the study area, is the major source of continental material; this is transported to sea in a benthic nepheloid layer and, mostly, alongshore to the southwest. Here, it largely leaves the shelf through the canyons, especially the Lacaze-Duthiers Canyon. In the offshore waters, particle concentrations and distributions show surficial, intermediate and benthic nepheloid layers. These turbid structures increase towards the southwest, corresponding to the seaward shift of the front between the coastal waters and the Liguro-Provençal cyclonic gyre, a major forcing function in the Gulf of Lions. Considering the source and fate of particles (largely biogenic from the euphotic zone and abiogenic from deeper waters) a layered system is described, which is emphasized by the concentrations of natural and artificial elements and compounds. Of the flux of particles to the Lacaze-Duthiers Canyon, on a decadal scale, about 30% (as a minimum) is estimated to be stored as sediment; the remainder is transported down-canyon, towards the deep sea. The temporal variability of processes affecting this net seaward transport, of both biogenic and abiogenic material, is from hours, days to seasonal, and probably interannual, time scales. The response of the system to these variations is rapid, with pulses of increased discharge of particles from the adjacent shelf being detected in sediment traps in the Lacaze-Duthiers Canyon in less than 16 days (the temporal resolution of the traps). Based upon the study of tracers of particulate matter and environmental factors (i.e. river discharge and climatic conditions), it appears that the contribution from the Rho^ne River and its adjacent area is maximal during the winter; at this time, the flow of the Liguro-Provençal Current also increases. In contrast, the maximum relative contribution of the adjacent southwesterly area to the flux in the Lacaze-Duthiers Canyon occurs in summer, during storm events.

Shoreline change on nine reef islands over a seven-decade period

Atoll islands are subject to a variety of processes that influence their geomorphological development. Analysis of historical shoreline changes using remotely sensed images has become an efficient approach to both quantify past changes and estimate future island response. However, the detection of long-term changes in beach width is challenging mainly for two reasons: first, data availability is limited for many remote Pacific islands. Second, beach environments are highly dynamic and strongly influenced by seasonal or episodic shoreline oscillations. Consequently, remote-sensing studies on beach morphodynamics of atoll islands deal with dynamic features covered by a low sampling frequency. Here we present a study of beach dynamics for nine islands on Takú Atoll, Papua New Guinea, over a seven-decade period. A considerable chronological gap between aerial photographs and satellite images was addressed by applying a new method that reweighted positions of the beach limit by identifying "outlier" shoreline positions. On top of natural beach variability observed along the reweighted beach sections, we found that one third of the analyzed islands show a statistically significant decrease in reweighted beach width since 1943. The total loss of beach area for all islands corresponds to 44% of the initial beach area. Variable shoreline trajectories suggest that changes in beach width on Takú Atoll are dependent on local control (that is, human activity and longshore sediment transport). Our results show that remote imagery with a low sampling frequency may be sufficient to characterize prominent morphological changes in planform beach configuration of reef islands.