Late Pliocene dinoflagellate cyst and diatom analysis from a high resolution sequence in DSDP Site 594, Chatham Rise, south west Pacific

A high resolution mixed carbonate and siliciclastic sequence from DSDP Site 594 contains a detailed record of climate change in the late Pliocene. The sequence can be accurately dated by the LAD of Nitzschia weaveri, the LAD of Thalassiosira insigna, the LAD of T. vulnifica and the LAD of T. kolbei diatom datums. Carbonate content and delta18O signatures provide added resolution and place the sequence between isotope stage 100 and 92. The sequence contains well-preserved and diverse dinoflagellate cyst floras. Use of principal component (PCA) and canonical correspondence analyses (CCA) identifies changes in the assemblages that principally reflect warming and cooling trends. Species association with warmer climates included Impagidinium patulum, I. paradoxum and I. sp. cf. paradoxum while those from cooler climates include Invertecysta tabulata and I. velorum. CCA is shown to be a valuable method of determining the past environmental preferences of extinct species such as I. tabulata.

High-resolution marine record of sediment core MD99-2343 in the Balearic Sea

The IMAGES core MD99-2343, recovered from a sediment drift north of the island of Minorca, in the north-western Mediterranean Sea, holds a high-resolution sequence that is perfectly suited to study the oscillations of the overturning system of the Western Mediterranean Deep Water (WMDW). Detailed analysis of grain-size and bulk geochemical composition reveals the sensitivity of this region to climate changes at both orbital and centennial-millennial temporal scales during the last 50 kyr. The dominant orbital pattern in the K/Al record indicates that sediment supply to the basin was controlled by the insolation evolution at 40°N, which forced changes in the fluvial regime, with more efficient sediment transport during insolation maxima. This orbital control also modulated the long-term pattern of the WMDW intensity as illustrated by the silt/clay ratio. However, deep convection was particularly sensitive to climatic changes at shorter time-scales, i.e. to centennial-millennial glacial and Holocene oscillations that are well documented by all the paleocurrent intensity proxies (Si/Al, Ti/Al and silt/clay ratios). Benthic isotopic records (d13C and d18O) show a Dansgaard-Oeschger (D-O) pattern of variability of WMDW properties, which can be associated with changing intensities of the deep currents system. The most prominent reduction on the WMDW overturning was caused by the post-glacial sea level rise. Three main scenarios of WMDW overturning are revealed: a strong mode during D-O Stadials, a weak mode during D-O Interstadials and an intermediate mode during cooling transitions. In addition, D-O Stadials associated with Heinrich events (HEs) have a very distinct signature as the strong mode of circulation, typical for the other D-O Stadials, was never reached during HE due to the surface freshening induced by the inflowing polar waters. Consequently, the WMDW overturning system oscillated around the intermediate mode of circulation during HE. Though surface conditions were more stable during the Holocene, the WMDW overturning cell still reacted synchronously to short-lived events, as shown by increments in the planktonic d18O record, triggering quick reinforcements of the deep water circulation. Overall, these results highlight the sensitivity of the WMDW to rapid climate change which in the recent past were likely induced by oceanographic and atmospheric reorganizations in the North Atlantic region.

High-resolution in situ oxygen microprofiles, porewater and solid phase geochemistry from the Crimean shelf (Black Sea) from Maria S. Merian cruise MSM15/1

The outer western Crimean shelf of the Black Sea is a natural laboratory to investigate effects of stable oxic versus varying hypoxic conditions on seafloor biogeochemical processes and benthic community structure. Bottom-water oxygen concentrations ranged from normoxic (175 µmol O2/L) and hypoxic (< 63 µmol O2/L) or even anoxic/sulfidic conditions within a few kilometers' distance. Variations in oxygen concentrations between 160 and 10 µmol/L even occurred within hours close to the chemocline at 134 m water depth. Total oxygen uptake, including diffusive as well as fauna-mediated oxygen consumption, decreased from 15 mmol/m**2/d on average in the oxic zone, to 7 mmol/m**2/d on average in the hypoxic zone, correlating with changes in macrobenthos composition. Benthic diffusive oxygen uptake rates, comprising respiration of microorganisms and small meiofauna, were similar in oxic and hypoxic zones (on average 4.5 mmol/m**2/d), but declined to 1.3 mmol/m**2/d in bottom waters with oxygen concentrations below 20 µmol/L. Measurements and modeling of porewater profiles indicated that reoxidation of reduced compounds played only a minor role in diffusive oxygen uptake under the different oxygen conditions, leaving the major fraction to aerobic degradation of organic carbon. Remineralization efficiency decreased from nearly 100 % in the oxic zone, to 50 % in the oxic-hypoxic zone, to 10 % in the hypoxic-anoxic zone. Overall, the faunal remineralization rate was more important, but also more influenced by fluctuating oxygen concentrations, than microbial and geochemical oxidation processes.

A 31,000-year high-resolution record from two sediment cores off northwest Africa

Benthic foraminiferal assemblage compositions and sedimentary geochemical parameters were analyzed in two radiocarbon dated sediment cores from the upwelling area off NW Africa at 12°N, to reconstruct productivity changes during the last 31 kyr. High-latitude cold events and variations in low-latitude summer insolation influenced humidity, wind systems, and the position of the tropical rain belt over this time period. This in turn caused changes in intensity and seasonality of primary productivity off the southern Northwest African continental margin. High accumulation rates of benthic foraminifera, carbonate, and organic carbon during times of north Atlantic melt water events Heinrich 2 (25.4 to 24.3 kyr BP) and 1 (16.8 to 15.8 kyr BP) indicate high productivity. Dominance of infaunal benthic foraminiferal species and high numbers of deep infaunal specimens during that time indicate a strong and sustained supply of refractory organic matter reworked from the upper slope and shelf. A more southerly position of the tropical rainbelt and the Northeast trade wind belt during Heinrich 2 and 1 may have enhanced wind intensity and almost permanent upwelling, driving this scenario. A phytodetritus-related benthic fauna indicates seasonally pulsed input of labile organic matter but generally low year-round productivity during the Last Glacial Maximum (23 to 18 kyr BP). The tropical rainbelt is more expanded to the North than during Heinrich Events, and relatively weak NE trade winds resulted in seasonal and weak upwelling, thus lower productivity. High productivity characterized by a seasonally high input of labile organic matter, is indicated for times of orbital forced warming, such as the African Humid Period (9.8 to 7 kyr BP). An intensified African monsoon during boreal summer and the northernmost position of the tropical rainbelt within the last 31 kyr resulted in enhanced river discharge from the northward-extended drainage area (or river basin) initiating intense phytoplankton blooms. In the late Holocene (4 to 0 kyr BP) strong carbonate dissolution may have been caused by even more enhanced organic matter fluxes to the sea floor. Increasing aridity on the continent and stronger NE trade winds induced intensive, seasonal coastal upwelling.

High resolution study of sediment core GeoB3606-1

Based on a high-resolution analysis of the diatom signal and biogenic bulk components at site GeoB3606-1 (25°S, off Namibia), we describe rapid palaeoceanographic changes in the Benguela Upwelling System (BUS) from early MIS 3 through to the early Holocene (55 000 to 7 000 14C yr BP). Coastal upwelling strongly varied at 25°S from MIS 3 through to MIS 2. The abrupt decrease in the accumulation rate of biogenic silica and diatoms from MIS 3 into MIS 2 records rapid oceanographic changes in the BUS off Namibia. During MIS 3, leakage of excess H4SiO4 acid from the Southern Ocean into low-latitude surface waters, as indicated by the occurrence of Antarctic diatoms, enhanced the production of spores of Chaetoceros at the expense of calcareous phytoplankton. Furthermore, shallower Antarctic Intermediate Water (AAIW) would have enriched the thermocline off Namibia with silicate transported from the Southern Ocean. The strong decrease of the siliceous signal throughout MIS 2 represents a decrease in the nutrient input to the BUS, even though the diatom assemblage is still dominated by spores of the upwelling-associated diatom genus Chaetoceros. Depletion of silicate in the thermocline from the onset of MIS 2 through to the early Holocene reflects the shutdown of AAIW injection from the Southern Ocean into the BUS, causing upwelled waters to become reduced in silicate, hence less favourable for diatom production. The deglaciation and early Holocene are characterised by the replacement of the upwelling-associated flora by a non-upwelling-related diatom community, reflecting weakened upwelling, retraction of the seaward extension of the chlorophyll filament off Lüderitz, and dominance of warmer waters.

Snow and ice surfaces on King George Island (Antarctic Peninsula) with high-resolution TerraSAR-X time series, with links to shapfiles and GeoTIFFs

Changes of glaciers and snow cover in polar regions affect a wide range of physical and ecosystem processes on land and in the adjacent marine environment. In this study, we investigate the potential of 11-day repeat high-resolution satellite image time series from the TerraSAR-X mission to derive glaciological and hydrological parameters on King George Island, Antarctica during the period Oct/25/2010 to Apr/19/2011. The spatial pattern and temporal evolution of snow cover extent on ice-free areas can be monitored using multi-temporal coherence images. SAR coherence is used to map glacier extent of land terminating glaciers with an average accuracy of 25 m. Multi-temporal SAR color composites identify the position of the late summer snow line at about 220 m above sea level. Glacier surface velocities are obtained from intensity feature-tracking. Surface velocities near the calving front of Fourcade Glacier were up to 1.8 ± 0.01 m/d. Using an intercept theorem based on fundamental geometric principles together with differential GPS field measurements, the ice discharge of Fourcade Glacier was estimated to 20700 ± 5500 m**3/d (corresponding to ~19 ± 5 kt/d). The rapidly changing surface conditions on King George Island and the lack of high-resolution digital elevation models for the region remain restrictions for the applicability of SAR data and the precision of derived products.

High-resolution stratigraphic framework for Mediterranean sapropel S5

A high-resolution stratigraphic framework is presented for sapropel S5, which represents the low-mid latitude climate optimum of the previous interglacial period (Eemian). The framework is based on three sites along a transect from west to east through the eastern Mediterranean, and is further validated using a fourth site. This method allows expression of S5-based proxy records of Eemian climate variability along a standardised depth scale that offers unprecedented possibilities for assessment of spatial gradients and signal leads and lags in an interval where highresolution (radiocarbon-style) dating cannot be performed. Our lateral comparison of S5 sapropels suggests that the onset of S5 in ODP site 967C (Eratosthenes seamount) was 1-6 centuries delayed relative to the onsets in more westerly sites.