Siliceous fossils in sediments of the Ibero-Moroccan shelf and adjacent deep sea plains

Siliceous skeletons were investigated in two core profiles (9 cores), one off Cap de Sines, Portugal and the other off Cap de Mazagan, Morocco. Total number of skeletons was determined per gram of dried sediment at different core depths of the fraction >21 µ. Results are compared with a core profile from the Arabian Sea. Diatoms are of four groups: (A) marine-planktonic, B) marine-benthic, (C) freshwater and (D) Tertiary species (Trinacria e.g.). Species from groups (B), (C) and (D) are redeposited in all cores taken at a water depth of greater than 100 m. Small numbers of Silicoflagellates and Radiolarians were found throughout the cores from the Ibero-Moroccan shelf. In the Arabian Sea core, Radiolarians were concentrated in distinct horizons in which Tertiary material was redeposited (40-50, 140-150, 250-260 cm). The number of siliceous skeletons per gram of dried sediment decreases more or less rapidly with increasing depth in all cores. Whereas about 2500 skeletons were found in sediments close to the surface, approximately 100 skeletons only were found in deeper (>40 cm) layers. Deeper horizons with more than 100 specimens were interpreted as redeposited material. This sediment contained robust skeletons, resistant against dissolution, as well as benthic and Tertiary material. The decrease of siliceous skeletons relative to core depth depends upon the sedimentation rate. Where the sedimentation rate is high, the opal dissolution zone extends down to 30-60 cm, where the sedimentation rate is low, it is located at 10-30 cm. Below these depths opals disappears. These zones also have approximately the same age (4000 years) everywhere. Siliceous skeletons dissolve differentially, first the Silicoflagellates disappear, second the Diatoms, third the Radiolarians, and fourth the Sponge Spicules. Surface structure of skeletons from near the opal dissolution zones are similar to those of skeletons treated with NaOH. Tertiary diatoms (Trinacria e. g.) and benthic diatoms (Campylodiscus e.g.) dissolve less rapidly than skeletons of modern planktonic diatoms (Coscinodiscus e.g.). The time control of the opal dissolution zones appeared rather independent of various oceanic influences. No evidence was found for effects from upwelling either off Portugal or off Morocco. No difference in dissolution rates was recorded between the abyssal plains lying off these two areas. Likewise, there was no change in solution rates from Pleistocene to Holocene within either one of the abyssal plains. The Mediterranean outflow, which is enriched in dissolved silica, apparently had no effect on dissolution rates of siliceous skeletons in the sediment.

Sea-surface reconstruction of the east-equatorial South Atlantic

In order to reconstruct Late Quatemary variations of surface oceanography in the eastequatorial South Atlantic, time series of sea-surface temperatures (SST) and paleoproductivity were established from cores recovered in the Guinea and Angola Basins, and at the Walvis Ridge. These records, based on sedimentary alkenone and organic carbon concentrations, reveal that during the last 350,000 years surface circulation and productivity changes in the east-equatorial South Atlantic were highiy sensitive to climate forcing at 23- and 100-kyr periodicities. Covarying SST and paleoproductivity changes at the equator and at the Walvis Ridge appear to be driven by variations in zonal trade-wind intensity, which forces intensification or reduction of coastal and equatorial upwelling, as well as enhanced Benguela cold water advection from the South. Phase relationships of precessional variations in the paleoproductivity and SST records from the distinct sites were evaluated with respect to boreal summer insolation over Africa, movements of southem ocean thermal fronts, and changes in global ice volume. The 23-kyr phasing implies a sensitivity of eastem South Atlantic surface water advection and upwelling to West African monsoon intensity and to changes in the position ofthe subtropical high pressure cell over the South Atlantic, both phenomena which modulate zonal strength of southeasterly trades. SST and productivity changes north of 20°S lack significant variance at the 41-kyr periodicity; and at the Walvis Ridge and the equator lead changes in ice volume. This may indicate that obliquity-driven clirnate change, characteristic for northem high latitudes, e.g fluctuations in continental ice masses, did not substantially influence subtropical and tropical surface circulation in the South Atlantic. At the 23-kyr cycle SST and productivity changes in the eastern Angola Basin lag those in the equatorial Atlantic and at the Walvis Ridge by about 3500 years. This lag is explained by variations in cross-equatorial surface water transport and west-east countercurrent retum flow modifying precessional variations of SST and productivity in the eastem Angola Basin relative to those in the mid South Atlantic area under the central field of zonal trade winds. Sea level-related shifts of upwelling cells in phase with global clirnate change may be also recorded in SST and productivity variability along the continental margin off Southwest Africa. They may account for the delay of the paleoceanogreaphic signal from continental margin sites with respect to that from the pelagic sites at the equator and the Walvis Ridge.

Terrain model of the eastern slope of the Porcupine Seabight (50 m grid size)

The topography of the eastern margin of the Porcupine Seabight was surveyed in June 2000 utilizing swath bathymetry. The survey was carried out during RV Polarstern cruise ANT XVII/4 as part of the GEOMOUND project. The main objective was to map and investigate the seafloor topography of this region. The investigated area contains a variability of morphological features such as deep sea channels and giant mounds. The survey was planned and realized on the basis of existing data so as to guarantee the complete coverage of the margin. In order to achieve a resolution of the final digital terrain model (DTM) that meets the project demands, data processing was adjusted accordingly. The grid spacing of the DTM was set to 50 m and an accuracy better than 1% of the water depth was achieved for 96% of the soundings.

Sea surface fugacity of carbon dioxide measurements in the Pacific ocean

As part of the JGOFS field program, extensive CO2 partial-pressure measurements were made in the atmosphere and in the surface waters of the equatorial Pacific from 1992 to 1999. For the first time, we are able to determine how processes occurring in the western portion of the equatorial Pacific impact the sea-air fluxes of CO2 in the central and eastern regions. These 8 years of data are compared with the decade of the 1980s. Over this period, surface-water pCO2 data indicate significant seasonal and interannual variations. The largest decreases in fluxes were associated with the 1991-94 and 1997-98 El Niño events. The lower sea-air CO2 fluxes during these two El Niño periods were the result of the combined effects of interconnected large-scale and locally forced physical processes: (1) development of a low-salinity surface cap as part of the formation of the warm pool in the western and central equatorial Pacific, (2) deepening of the thermocline by propagating Kelvin waves in the eastern Pacific, and (3) the weakening of the winds in the eastern half of the basin. These processes serve to reduce pCO2 values in the central and eastern equatorial Pacific towards near-equilibrium values at the height of the warm phase of ENSO. In the western equatorial Pacific there is a small but significant increase in seawater pCO2 during strong El Niño events (i.e., 1982-83 and 1997-98) and little or no change during weak El Niño events (1991-94). The net effect of these interannual variations is a lower-than-normal CO2 flux to the atmosphere from the equatorial Pacific during El Niño. The annual average fluxes indicate that during strong El Niños the release to the atmosphere is 0.2-0.4 Pg C/yr compared to 0.8-1.0 Pg C/yr during non-El Niño years.

(Table 1) Chlorophyll a content and microalgae abundance and biovolume in pack ice in the Bellingshausen Sea

Pack ice in the Bellingshausen Sea contained moderate to high stocks of microalgal biomass (3-10 mg Chl a/m**2) spanning the range of general sea-ice microalgal microhabitats (e.g., bottom, interior and surface) during the International Polar Year (IPY) Sea Ice Mass Balance in the Antarctic (SIMBA) studies. Measurements of irradiance above and beneath the ice as well as optical properties of the microalgae therein demonstrated that absorption of photosynthetically active radiation (PAR) by particulates (microalgae and detritus) had a substantial influence on attenuation of PAR and irradiance transmission in areas with moderate snow covers (0.2-0.3 m) and more moderate effects in areas with low snow cover. Particulates contributed an estimated 25 to 90% of the attenuation coefficients for the first-year sea ice at wavelengths less than 500 nm. Strong ultraviolet radiation (UVR) absorption by particulates was prevalent in the ice habitats where solar radiation was highest - with absorption coefficients by ice algae often being as large as that of the sea ice. Strong UVR-absorption features were associated with an abundance of dinoflagellates and a general lack of diatoms - perhaps suggesting UVR may be influencing the structure of some parts of the sea-ice microbial communities in the pack ice during spring. We also evaluated the time-varying changes in the spectra of under-ice irradiances in the austral spring and showed dynamics associated with changes that could be attributed to coupled changes in the ice thickness (mass balance) and microalgal biomass. All results are indicative of radiation-induced changes in the absorption properties of the pack ice and highlight the non-linear, time-varying, biophysical interactions operating within the Antarctic pack ice ecosystem.

AMS 14C dating points, isotopic compositions, Mg/Ca ratios and sea surface temperatures of sediment cores GeoB10029-4 and GeoB10038-4

Quantifying the spatial and temporal sea surface temperature (SST) and salinity changes of the Indo-Pacific Warm Pool is essential to understand the role of this region in connection with abrupt climate changes particularly during the last deglaciation. In this study we reconstruct SST and seawater d18O of the tropical eastern Indian Ocean for the past 40,000 years from two sediment cores (GeoB 10029-4, 1°30'S, 100°08'E, and GeoB 10038-4, 5°56'S, 103°15'E) retrieved offshore Sumatra. Our results show that annual mean SSTs increased about 2-3 °C at 19,000 years ago and exhibited southern hemisphere-like timing and pattern during the last deglaciation. Our SST records together with other Mg/Ca-based SST reconstructions around Indonesia do not track the monsoon variation since the last glacial period, as recorded by terrestrial monsoon archives. However, the spatial SST heterogeneity might be a result of changing monsoon intensity that shifts either the annual mean SSTs or the seasonality of G. ruber towards the warmer or the cooler season at different locations. Seawater d18O reconstructions north of the equator suggest fresher surface conditions during the last glacial and track the northern high-latitude climate change during the last deglaciation. In contrast, seawater ?18O records south of the equator do not show a significant difference between the last glacial period and the Holocene, and lack Bølling-Allerød and Younger Dryas periods suggestive of additional controls on annual mean surface hydrology in this part of the Indo-Pacific Warm Pool.

Sea surface fugacity of carbon dioxide measurements in the Indian and Southern Oceans obtained during MINERVE-29/ANTARES-II cruise

The sub-Antarctic zone (SAZ) lies between the subtropical convergence (STC) and the sub-Antarctic front (SAF), and is considered one of the strongest oceanic sinks of atmospheric CO2. The strong sink results from high winds and seasonally low sea surface fugacities of CO2 (fCO2), relative to atmospheric fCO2. The region of the SAZ, and immediately south, is also subject to mode and intermediate water formation, yielding a penetration of anthropogenic CO2 below the mixed layer. A detailed analysis of continuous measurements made during the same season and year, February - March 1993, shows a coherent pattern of fCO2 distributions at the eastern (WOCE/SR3 at about 145°E) and western edges (WOCE/I6 at 30°E) of the Indian sector of the Southern Ocean. A strong CO2 sink develops in the Austral summer (delta fCO2 < - 50 µatm) in both the eastern (110°-150°E) and western regions (20°-90°E). The strong CO2 sink in summer is due to the formation of a shallow seasonal mixed-layer (about 100 m). The CO2 drawdown in the surface water is consistent with biologically mediated drawdown of carbon over summer. In austral winter, surface fCO2 is close to equilibrium with the atmosphere (delta fCO2 ± 5 µatm), and the net CO2 exchange is small compared to summer. The near-equilibrium values in winter are associated with the formation of deep winter mixed-layers (up to 700 m). For years 1992-95, the annual CO2 uptake for the Indian Ocean sector of the sub Antarctic Zone (40°-50°S, 20°-150°E) is estimated to be about 0.4 GtC/yr. Extrapolating this estimate to the entire sub-Antarctic zone suggests the uptake in the circumpolar SAZ is approaching 1 GtC/yr.

(Table 1) Summary statistics of in situ sea-ice characteristics of Ice Station Belgica sites Fabra, Patria/Liège and Brussels in October 2007

Three ice type regimes at Ice Station Belgica (ISB), during the 2007 International Polar Year SIMBA (Sea Ice Mass Balance in Antarctica) expedition, were characterized and assessed for elevation, snow depth, ice freeboard and thickness. Analyses of the probability distribution functions showed great potential for satellite-based altimetry for estimating ice thickness. In question is the required altimeter sampling density for reasonably accurate estimation of snow surface elevation given inherent spatial averaging. This study assesses an effort to determine the number of laser altimeter 'hits' of the ISB floe, as a representative Antarctic floe of mixed first- and multi-year ice types, for the purpose of statistically recreating the in situ-determined ice-thickness and snow depth distribution based on the fractional coverage of each ice type. Estimates of the fractional coverage and spatial distribution of the ice types, referred to as ice 'towns', for the 5 km**2 floe were assessed by in situ mapping and photo-visual documentation. Simulated ICESat altimeter tracks, with spot size ~70 m and spacing ~170 m, sampled the floe's towns, generating a buoyancy-derived ice thickness distribution. 115 altimeter hits were required to statistically recreate the regional thickness mean and distribution for a three-town assemblage of mixed first- and multi-year ice, and 85 hits for a two-town assemblage of first-year ice only: equivalent to 19.5 and 14.5 km respectively of continuous altimeter track over a floe region of similar structure. Results have significant implications toward model development of sea-ice sampling performance of the ICESat laser altimeter record as well as maximizing sampling characteristics of satellite/airborne laser and radar altimetry missions for sea-ice thickness.

Physical oceanography from eight Seaglider missions in the Mediterranean Sea, Eastern Basin

In 2008, the Oceanography Center at the University of Cyprus acquired two underwater gliders in the framework of a nationally-managed infrastructure upgrade program. The gliders were purchased from the Seaglider Fabrication Center at the University of Washington. Both gliders are rated to 1000 m and carry a typical sensor payload: non-pumped conductivity-temperature-depth sensors (CTD), a dissolved oxygen sensor, an optical triplet to measure optical backscatter at 400 nm, 700 nm, and chlorophyll-a fluorescence. Since March of 2009, the gliders have been used in a long-term observing program of the Cypriot EEZ, and by September 2015, have covered more than 15300 km over ground and 3500 dive cycles in 940 glider days. Butterfly patterns have been flown in two configurations, either on the western or eastern side of the EEZ south of Cyprus. The glider endurance lines criss-cross the region in order to more accurately locate and investigate the mesoscale structures south of Cyprus, and in particular the Cyprus eddy which is often the dominant feature. Based on the near real time observations, the glider mission was sometimes altered in order to more fully sample the Cyprus eddy, or to locate its center or extent. A summary of the raw and processed data collected, and the quality control procedures are presented, in order for future users to take advantage of this unique data set.