Seawater carbonate chemistry and processes during experiments with coccolithophores (Emiliania huxleyi and Gephyrocapsa oceanica), 2000

The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments1. This is important in regulating marine carbon cycling and ocean-atmosphere CO2 exchange2. The present rise in atmospheric CO2 levels3 causes significant changes in surface ocean pH and carbonate chemistry4. Such changes have been shown to slow down calcification in corals and coralline macroalgae5,6, but the majority of marine calcification occurs in planktonic organisms. Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species, the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica . This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres. Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production. Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels. We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean. As the process of calcification releases CO2 to the atmosphere, the response observed here could potentially act as a negative feedback on atmospheric CO2 levels.

Fresh biomass of macroalgae collected at Hansneset, Kongsfjorden, Spitsbergen in 1996/1998

We surveyed macroalgae at Hansneset, Blomstrand in Kongsfjorden, Svalbard, down to 30 m depth between 1996 and 1998. In total, 62 species were identified: 16 Chlorophyta, 25 Phaeophyceae, and 21 Rhodophyta. The majority of species (53.5%) belonged to the Arctic cold-temperate group, followed in frequency by species distributed from the Arctic to the warm-temperate region (25.9%). Four endemic Arctic species (Laminaria solidungula, Acrosiphonia flagellata, A. incurva, and Urospora elongata) were found. Two species (Pogotrichum filiforme and Mikrosyphar polysiphoniae) were new to Svalbard. Chlorophyta, Phaeophyceae, and Rhodophyta extended from the eulittoral zone down to 11, 21, and >30 m depths with maximum biomasses at 1-5 m, 5-10 m, and 5-30 m depths, respectively. Annual and pseudoperennial species had highest biomasses in the upper 5 m, while perennials were distributed deeper. The highest biomass (8600 g/m**2 wet weight) at 5 m depth comprised mainly L. digitata, Saccorhiza dermatodea, Alaria esculenta, and Saccharina latissima. The biogeographic composition of macroalgae at Hansneset was rather similar to that of northeastern Greenland, but different from that of northern Norway, which has a higher proportion of temperate species. Climate warming and ship traffic may extend some of the distribution ranges of macroalgae from mainland Norway to Svalbard.

(Appendix B) Benthic foraminifera in Indian Ocean surface sediments

Multivariate analysis was performed on percentages of 46 species of unstained deep-sea benthic foraminifera from 131 core-top to near-core-top samples (322-5013 m) from across the Indian Ocean. Faunal data are combined with GEOSECS geochemical data to investigate any relationship between benthic foraminifera (assemblages and species) and deep-sea properties. In general, benthic foraminifera show a good correlation to surface productivity, organic carbon flux to the sea floor, deep-sea oxygenation and, to a lesser extent, to bottom temperature, without correlation with the water depths. The foraminiferal census data combined with geochemical data has enabled the division of the Indian Ocean into two faunal provinces. Province A occupies the northwestern Indian Ocean (Arabian Sea region) where surface primary production has a major maximum during the summer monsoon season and a secondary maximum during winter monsoon season that leads to high organic flux to the seafloor, making the deep-sea one of the most oxygen-deficient regions in the world ocean, with a pronounced oxygen minimum zone (OMZ). This province is dominated by benthic foraminifera characteristic of low oxygen and high organic food flux including Uvigerina peregrina, Robulus nicobarensis, Bolivinita pseudopunctata, Bolivinita sp., Bulimina aculeata, Bulimina alazanensis, Ehrenbergina carinata and Cassidulina carinata. Province B covers southern, southeastern and eastern parts of the Indian Ocean and is dominated by Nuttallides umbonifera, Epistominella exigua, Globocassidulina subglobosa, Uvigerina proboscidea, Cibicides wuellerstorfi, Cassidulina laevigata, Pullenia bulloides, Pullenia osloensis, Pyrgo murrhina, Oridorsalis umbonatus, Gyroidinoides (= Gyroidina) soldanii and Gyroidinoides cf. gemma suggesting well-oxygenated, cold deep water with low (oligotrophic) and pulsed food supply.

Benthic foraminifera in eastern equatorial Indian Ocean surface sediments

Study of Recent abyssal benthic foraminifera from core-top samples in the eastern equatorial Indian Ocean has identified distinctive faunas whose distribution patterns reflect the major hydrographic features of the region. Above 3800 m, Indian Deep Water (IDW) is characterized by a diverse and evenly-distributed biofacies to which Globocassidulina subglobosa, Pyrgo spp., Uvigerina peregrina, and Eggerella bradyi are the major contributors. Nuttalides umbonifera and Epistominella exigua are associated with Indian Bottom Water (IBW) below 3800 m. Within the IBW fauna, N. umbonifera and E. exigua are characteristic of two biofacies with independent distribution patterns. Nuttalides umbonifera systematically increases in abundance with increasing water depth. The E. exigua biofacies reaches its greatest abundance in sediments on the eastern flank of the Ninetyeast Ridge and in the Wharton-Cocos Basin. The hydrographic transition between IDW and IBW coincides with the level of transition from waters supersaturated to waters undersaturated with respect to calcite and with the depth of the lysocline. Carbonate saturation levels, possibly combined with the effects of selective dissolution on the benthic foraminiferal populations, best explain the change in faunas across the IDW/IBW boundary and the bathymetric distribution pattern of N. umbonifera. The distribution of the E. exigua fauna cannot be explained with this model. Epistominella exigua is associated with the colder, more oxygenated IBW of the Wharton-Cocos Basin. The distribution of this biofacies on the eastern flank of the Ninetyeast Ridge agrees well with the calculated bathymetric position of the northward flowing deep boundary current which aerates the eastern basins of the Indian Ocean.

Benthic foraminifera in Southwest Indian Ocean surface sediments

The distribution of deep-sea benthonic foraminifera in core top samples from the southwest Indian Ocean is examined. Principal component analysis reveals two major assemblages. One assemblages between 3600 and 4800-m water depth is dominated by Episominella umbonifera and is associated with cold (Theta = -0.3 to 0.8°C), low salinity (34.66 to 34.72 * 10**-3) Antarctic Bottom Water in the Crozet Basin, in fracture zones, and on the flanks of the Southwest Indian Ridge. A second assemblage, dominated by Planulina wuellerstorfi, Globocassidulina subglobasa, Astrononion echolsi and Pullenia bulloides, is between 1600 and 3800 m on the Crozet Plateau, Madagascar Ridge, Central Indian Ridge, and Southwest Indian Ridge and is associated with relatively warm (Theta = 0.8 to 2.6°C), high salinity (34.72 to 34.76 * 10**-3) North Atlantic Deep Water. The third principal component divides the P. wuellerstorfi assemblage into two subgroups. One is dominated by Epistominella exigua, P. bulloides, P. wuellerstorfi, and A. echolsi and a second is dominated by G. subglobosa. The distribution of the E. umbonifera assemblage and previous hydrographic studies suggest that AABW flows as a western boundary contour current in the Crozet Basin and penetrates fracture zones in the Southwest Indian Ridge between 55 and 57°E and near 66°E as it travels northward into the Madagascar and Mascarene basins. The faunal-water mass associations from the southeast Indian Ocean are compared; the most notable faunal difference is the absence of Uvigerina as a dominant taxon in the southwest Indian Ocean. A comparison of dissolved oxygen and Uvigerina data shows that oxygen is not a major influence upon the distribution of Uvigerina. A correlation analysis of the faunal data and water depth, potential temperature, in situ temperature, salinity, dissolved oxygen, and 1 - Omega, an index of calcium carbonate undersaturation, was carried out to determine the relationships between fauna and hydrography. The second principal component has a significant positive correlation at the 99.9% level with temperature and negative correlations with water depth and 1 - Omega. A general faunal-water mass correlation exists, but it is not possible to determine which variable controls the faunal distributions.

Radiolarian abundance of sediment core Y8

A high-resolution record of radiolarian faunal changes from Site Y8 south of the Subtropical Front (STF), offshore eastern New Zealand, provides insight into the paleoceanographic history of the last 265 kyrs. Quantitative analysis of radiolarian paleotemperature indicators and radiolarian-based sea surface temperature (SST) estimates reveal distinct shifts during glacial-interglacial (G-I) climate cycles encompassing marine isotope stages (MIS) 8-1. Faunas at Site Y8 are abundant and diverse and consist of a mixture of species typical of the subantarctic, transitional and subtropical zones which is characteristic of subantarctic waters just south of the STF. During interglacials, diverse radiolarian faunas have increased numbers of warm-water taxa (not, vert, similar 15%) while cool-water taxa decrease to not, vert, similar 11% of the assemblage. Warmest climate conditions occurred during MIS 5.5 and the early Holocene Climatic Optimum (HCO) at the onset of MIS 1 where SSTs reach maxima of 12.8 and 12.9 °C, respectively. This suggests that temperatures during the HCO were comparable to the Eemian, one of the warmest interglacial intervals of the Late Quaternary. Glacials are characterized by less diverse radiolarian faunas with cool-water taxa increasing to 49% of the assemblage. Coolest climate conditions occurred in MIS 4 and 2 where SSTs are reduced to 5.4 °C and 4.3 °C, respectively. Radiolarian faunal changes and SST estimates clearly identify major water masses and oceanic fronts in the offshore eastern New Zealand area. During warmest MIS 5.5 and early MIS 1 substantial influence of northern-sourced Subtropical Surface Water (STW) is evident at Site Y8. This implies southward incursions of STW around the eastern crest of Chatham Rise with the STF displaced towards higher latitudes and spinning off eddies as far south as Campbell Plateau. Additionally, increased flow of the Southland Current (SC) might have enhanced the local occurrence of warm-water radiolarians derived from the subtropical Tasman Sea. Coolest glacials are marked by a strong inflow of cool, southern-sourced waters at Site Y8 indicating a more vigorous flow along the Subantarctic Front (SAF).

Standing stocks and carbon isotopes of live benthic foraminifera from the South Atlantic

Live (Rose Bengal stained) and dead benthic foraminifera of surface and subsurface sediments from 25 stations in the eastern South Atlantic Ocean and the Atlantic sector of the Southern Ocean were analyzed to decipher a potential influence of seasonally and spatially varying high primary productivity on the stable carbon isotopic composition of foraminiferal tests. Therefore, stations were chosen so that productivity strongly varied, whereas conservative water mass properties changed only little. To define the stable carbon isotopic composition of dissolved inorganic carbon (d13CDIC) in ambient water masses, we compiled new and previously published d13CDIC data in a section running from Antarctica through Agulhas, Cape and Angola Basins, via the Guinea Abyssal Plain to the Equator. We found that intraspecific d13C variability of all species at a single site is constantly low throughout their distribution within the sediments, i.e. species specific and site dependent mean values calculated from all subbottom depths on average only varied by +/-0.09 per mil. This is important because it makes the stable carbon isotopic signal of species independent of the particular microhabitat of each single specimen measured and thus more constant and reliable than has been previously assumed. So-called vital and/or microhabitat effects were further quantified: (1) d13C values of endobenthic Globobulimina affinis, Fursenkoina mexicana, and Bulimina mexicana consistently are by between -1.5 and -1.0 per mil VPDB more depleted than d13C values of preferentially epibenthic Fontbotia wuellerstorfi, Cibicidoides pachyderma, and Lobatula lobatula. (2) In contrast to the Antarctic Polar Front region, at all stations except one on the African continental slope Fontbotia wuellerstorfi records bottom water d13CDIC values without significant offset, whereas L. lobatula and C. pachyderma values deviate from bottom water values by about -0.4 per mil and -0.6 per mil, respectively. This adds to the growing amount of data on contrasting cibicid d13C values which on the one hand support the original 1:1-calibration of F. wuellerstorfi and bottom water d13CDIC, and on the other hand document severe depletions of taxonomically close relatives such as L. lobatula and C. pachyderma. At one station close to Bouvet Island at the western rim of Agulhas Basin, we interpret the offset of -1.5 per mil between bottom water d13CDIC and d13C values of infaunal living Bulimina aculeata in contrast to about -0.6 +/- 0.1 per mil measured at eight stations close-by, as a direct reflection of locally increased organic matter fluxes and sedimentation rates. Alternatively, we speculate that methane locally released from gas vents and related to hydrothermal venting at the mid-ocean ridge might have caused this strong depletion of 13C in the benthic foraminiferal carbon isotopic composition. Along the African continental margin, offsets between deep infaunal Globobulimina affinis and epibenthic Fontbotia wuellerstorfi as well as between shallow infaunal Uvigerina peregrina and F. wuellerstorfi, d13C values tend to increase with generally increasing organic matter decomposition rates. Although clearly more data are needed, these offsets between species might be used for quantification of biogeochemical paleogradients within the sediment and thus paleocarbon flux estimates. Furthermore, our data suggest that in high-productivity areas where sedimentary carbonate contents are lower than 15 weight %, epibenthic and endobenthic foraminiferal d13C values are strongly influenced by 13C enrichment probably due to carbonate-ion undersaturation, whereas above this sedimentary carbonate threshold endobenthic d13C values reflect depleted pore water d13CDIC values.

Recent benthic foraminifera of the Scotia Sea and Argentine Basin

We investigated 88 surface sediment samples taken with a multiple corer from the southwestern South Atlantic Ocean for their live (Rose Bengal stained) and dead benthic foraminiferal content. Using Q-Mode Principal Component Analysis six live and six dead associations are differentiated. Live and dead association distributions correspond fairly well; differences are mainly caused by downslope transport and selective test destruction. In addition, four potential fossil associations are calculated from the dead data set after removal of non-fossilizable species. These potential fossil associations are expected to be useful for paleoceanographic reconstructions. Environments are described in detail for the live and potential fossil associations and for selected species. Along the upper Argentine continental slope strong bottom currents control the occurrence of live, dead and potential fossil Angulogerina angulosa associations. Here, particles of a high organic carbon flux rate remain suspended. Below this high energy environment live, dead and potential fossil Uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates. The live A. angulosa and U. peregrina associations correlate with high standing crops. Furthermore, live and dead Epistominella exigua-Nuttallides umbonifer associations were separated. Dominance of a Nuttallides umbonifer potential fossil association relates to coverage by Antarctic Bottom Water (AABW) and Lower Circumpolar Deep Water (LCDW), above the Calcite Compensation Depth (CCD). Three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by AABW or CDW. A Reophax difflugiformis association was found in mud-rich and diatomaceous sediments. Below the CCD, a Psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a Cribrostomoides subglobosus-Ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30%. One single Eggerella bradyi-Martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the CCD if only preservable species are considered for calculation.

Distribution of diatoms, coccolithophores and planktic foraminifera in the Arabian Sea

The distribution of diatoms, coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean (0-100 m) across the upwelling area off the Oman coast to the central Arabian Sea during May/June 1997 and July/August 1995. The number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration (nitrate, phosphate, silicate) caused by upwelling. Vegetative cells of Chaetoceros dominated the diatom assemblage in the coastal upwelling area. Towards the more nutrient depleted and stratified surface waters to the southeast, the number of diatoms decreased, coccolithophore and planktic foraminiferal numbers increased, and floral and faunal composition changed. In particular, the transition between the eutrophic upwelling region off Oman and the oligotrophic central Arabian Sea was marked by moderate nutrient concentration, and high coccolithophore and foraminifer numbers. Florisphaera profunda, previously often referred as a 'lower-photic-zone-species', was frequent in water depths as shallow as 20 m, and at high nutrient concentration up to 14 µmol NO3/l and 1.2 µmol PO4/. To the oligotrophic southeast of the divergence, cell densities of coccolithophores declined and Umbellosphaera irregularis prevailed throughout the water column down to 100 m depth. In general, total coccolithophore numbers were limited by nutrient threshold concentration, with low numbers (<10*10**3 cells/l) at high [NO3] and [PO4], and high numbers (>70*10**3 cells/l) at low [NO3] and [PO4]. The components of the complex microplankton succession, diatoms, coccoliths and planktic foraminifers (and possibly others), should ideally be used as a combined paleoceanographic proxy. Consequently, models on plankton ecology should be resolved at least for the seasonality, to account for the bias of paleoceanographic transfer calculations.

(Appendix A) Radiolarian abundance in ODP Hole 202-1241A

A quantitative radiolarian study at Ocean Drilling Program Site 1241 in the eastern tropical Pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle Miocene. Today, this site is located just under the Eastern Pacific Warm Pool (EPWP). Based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes, it is suggested that three notable changes occurred at 10.6, 9.8, and 4.2 Ma in the region. Four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following: (1) stratified seawater (12.0 to 10.6 Ma); (2) a shallowing of the thermocline and an increasing of upwelling (10.6 to 9.8 Ma); (3) significant inflow of warm water to the eastern tropical Pacific caused by an intensified Northern Equatorial Countercurrent (NECC), resulting in the formation of EPWP (9.8 to 4.2 Ma); and (4) the reduction of the EPWP and the NECC, and an increase in upwelling (4.2 to 0 Ma). The timing of these paleoceanographic events indicated the strong relations with the opening and closing of the Indonesian and Central American (Panama) Seaways. The reduction of the EPWP (this study) and the deepening of the thermocline in western Pacific at about 4.2 Ma (Cannariato and Ravelo, 1997; Chaisson and Ravelo, 2000) indicated a change from a state resembling El Niño in the late Miocene and the early Pliocene time to a state resembling La Niña by the late Pliocene

Benthic foraminifera asemblages and isotopic composition of surface sediment samples off Morocco

The influence of different primary productivity regimes on live (Rose Bengal stained) and dead benthic foraminiferal distribution, as well as on the stable carbon isotopic composition of foraminiferal tests, was investigated in sediment surface samples (0-1 cm) from the upwelling region off Morocco between Cape Ghir (31°N) and Cape Yubi (27°N). A combination of factor analysis, detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) was applied to the benthic foraminiferal data sets. Five major assemblages for both the live and dead fauna were revealed by factor analysis. In the cape regions organic matter fluxes are enhanced by high chlorophyll-a concentrations in the overlying surface waters. Here, benthic foraminiferal faunas are characterized by identical live and dead assemblages, high standing stocks, and low species delta13C values, indicating constant year-round high productivity. Bulimina marginata dominates the unique fauna at the shallowest station off Cape Ghir indicating highest chlorophyll-a concentrations. Off both capes, the succession of the Bulimina aculeata/Uvigerina mediterranea assemblage, the Sphaeroidina bulloides/Gavelinopsis translucens assemblage, and the Hoeglundina elegans assemblage from the shelf to the deep sea reflects the decrease in chlorophyll-a concentrations, hence the export flux. In contrast, the area between the capes is characterized by differently composed live and dead assemblages, low standing stocks, and less depleted delta13C values, thus reflecting low primary productivity. High foraminiferal numbers of Epistominella exigua, Eponides pusillus, and Globocassidulina subglobosa in the dead fauna indicate a seasonally varying primary productivity signal. Significantly lower mean delta13C values were recorded in Bulimina mexicana, Cibicidoides kullenbergi, H. elegans, U. mediterranea and Uvigerina peregrina. Cibicidoides wuellerstorfi is a faithful recorder of bottom water delta13C in the Canary Islands regions. The mean delta13C signal of this species is not significantly influenced by constant high organic matter fluxes. The species-specific offset between live and dead specimens is the same.

Lower Albian benthic foraminifera

The Early Albian Oceanic Anoxic Event 1b (OAE 1b) black shale is interrupted by one or more ventilation events that display significant changes in benthic and planktic populations. Within the OAE 1b sections studied, at ODP Site 1049, DSDP Site 545, and the Vocontian Basin, the benthic foraminiferal repopulation events last between ~500 and ~1,250 years and occur with a cyclicity of approximately 5.7 kyr. This period may represent an amplitude modulation of the precessional cycle. The OAE 1b sections from the marginal setting of the Vocontian Basin exhibit up to eight repopulation events. In contrast, there is only one repopulation event identified in the Atlantic OAE 1b sections from the Mazagan Plateau (DSDP 545) and Blake Nose (ODP 1049). Within the margin of dating uncertainties, this supraregional repopulation event occurred synchronously in the Vocontian Basin and the Atlantic Ocean. While the OAE 1b black shale formed under extremely warm and humid conditions, the repopulation events occurred during intervals of short-term cooling and reduced humidity at deep-water formation sites. The resulting increase in evaporation led to enhanced formation of low-latitude deep water, thus improving the ventilation of the sea floor.

Benthic foraminifera assemblages of the Gulf of Aden

Benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the Gulf of Aden, NW Arabian Sea that spans the last 530 ka. The benthic foraminifera were grouped into four principal assemblages using Q-mode Principal Component Analyses. Comparison of each of these assemblages with the fauna of the nearby regions enabled us to identify their specific environmental requirements as a function of variability in food supply and strength of the oxygen minimum zone and by that to use them as indicators of surface water productivity. The benthic foraminiferal productivity indicators coupled with the record of Globigerina bulloides, a planktic foraminifer known to be sensitive to productivity changes in the region, all indicate higher productivity during glacial intervals and productivity similar to present or even reduced during interglacial stages. This trend is opposite to the productivity pattern related to the SW summer monsoon of the Arabian Sea and indicates the role of the NE winter monsoon on the productivity of the Gulf of Aden. A period of exceptionally enhanced productivity is recognized in the Gulf of Aden region between ~60 and 13 kyr indicating the intensification of the NE winter monsoon to its maximal activity. Contemporaneous indication of increased productivity in other parts of the Arabian Sea, unexplained so far by the SW summer monsoon variability, might be related to the intensification of the NE winter monsoon. Another prominent event of high productivity, second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr. These two events seem to correspond to periods of similar orbital positioning of rather low precession (and eccentricity) amplitude for a relatively long period. Glacial boundary conditions seem to control to a large extent the NE winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series. Secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the NE monsoonal variability. Following the identification of productivity events related to the NE winter monsoon in the Gulf of Aden, it is possible now to extend this observation to other parts of the Arabian Sea and consider the contribution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records.