Survey Cruises Research Articles

Horizontal and vertical distribution of euphausiid species on the Western Antarctic Peninsula U.S. GLOBEC Southern Ocean study site

The Western Antarctic Peninsula (WAP) is a site of high krill abundance and a likely source region for krill populations found to the north and east of the area. The U.S. GLOBEC Southern Ocean program studied factors that contribute to the overwintering success of krill in the region of Marguerite Bay, WAP. A MOCNESS net system was used to sample the vertical distribution and abundance of zooplankton relative to physical features (hydrography and circulation) during four broad-scale survey cruises in the fall and winter of 2001 and 2002. Four species were found throughout the study area on all four cruises: Euphausia superba, Euphausia crystallorophias, Euphausia triacantha, and Thysanoessa macrura. The species had significantly different horizontal and vertical distributions. Both E. superba and T. macrura were broadly distributed throughout the area, but the central 50% of their vertical distributions were distinct with E. superba most abundant in the upper 100 m in the coldest, freshest water (average temperature and salinity: −1.13 °C; 33.80) and T. macrura occurring between 100 and 250 m (at 0.01 °C; 34.228). E. crystallorophias had a more coastal distribution and was usually found deeper in slightly warmer and saltier water (−0.44 °C; 33.9982) than E. superba and either overlapped or was above T. macrura in depth. E. triacantha was much rarer and sporadically distributed in the study area and was found substantially deeper (center of distribution about 300 m) in the warmest saltiest water (1.40 °C; 34.65) than the other three euphausiid species. Larval distributions for E. superba indicated that at least some proportion of the populations resulted from reproduction and development on the continental shelf, and not solely from offshore reproduction and transport onto the shelf. A neutral particle tracking model was used to gain insight into the relative importance of shelf versus off-shelf origins for the larvae. The results suggest that a combination of offshore and onshore reproduction can account for the observed E. superba larval distributions in the U.S. SO GLOBEC study site.

Spatial analysis of egg distribution and geographic changes in the spawning habitat of the Brazilian sardine Sardinella brasiliensis

This paper establishes the spawning habitat of the Brazilian sardine Sardinella brasiliensis and investigates the spatial variability of egg density and its relation with oceanographic conditions in the shelf of the south-east Brazil Bight (SBB). The spawning habitats of S. brasiliensis have been defined in terms of spatial models of egg density, temperature-salinity plots, quotient (Q) analysis and remote sensing data. Quotient curves (Q(C)) were constructed using the geographic distribution of egg density, temperature and salinity from samples collected during nine survey cruises between 1976 and 1993. The interannual sea surface temperature (SST) variability was determined using principal component analysis on the SST anomalies (SSTA) estimated from remote sensing data over the period between 1985 and 2007. The spatial pattern of egg occurrences in the SBB indicated that the largest concentration occurred between Paranaguá and São Sebastião. Spawning habitat expanded and contracted during the years, fluctuating around Paranaguá. In January 1978 and January 1993, eggs were found nearly everywhere along the inner shelf of the SBB, while in January 1988 and 1991 spawning had contracted to their southernmost position. The SSTA maps for the spawning periods showed that in the case of habitat expansion (1993 only) anomalies over the SBB were zero or slightly negative, whereas for the contraction period anomalies were all positive. Sardinella brasiliensis is capable of exploring suitable spawning sites provided by the entrainment of the colder and less-saline South Atlantic Central Water onto the shelf by means of both coastal wind-driven (to the north-east of the SBB) and meander-induced (to the south-west of the SBB) upwelling.

The combined effects of ocean acidification, mixing, and respiration on pH and carbonate saturation in an urbanized estuary

Puget Sound is a large estuary complex in the U.S. Pacific Northwest that is home to a diverse and economically important ecosystem threatened by anthropogenic impacts associated with climate change, urbanization, and ocean acidification. While ocean acidification has been studied in oceanic waters, little is known regarding its status in estuaries. Anthropogenically acidified coastal waters upwelling along the western North American continental margin can enter Puget Sound through the Strait of Juan de Fuca. In order to study the combined effects of ocean acidification and other natural and anthropogenic processes on Puget Sound waters, we made the first inorganic carbon measurements in this estuary on two survey cruises in February and August of 2008. Observed pH and aragonite saturation state values in surface and subsurface waters were substantially lower in parts of Puget Sound than would be expected from anthropogenic carbon dioxide (CO 2) uptake alone. We estimate that ocean acidification can account for 24–49% of the pH decrease in the deep waters of the Hood Canal sub-basin of Puget Sound relative to estimated pre-industrial values. The remaining change in pH between when seawater enters the sound and when it reaches this deep basin results from remineralization of organic matter due to natural or anthropogenically stimulated respiration processes within Puget Sound. Over time, however, the relative impact of ocean acidification could increase significantly, accounting for 49–82% of the pH decrease in subsurface waters for a doubling of atmospheric CO 2. These changes may have profound impacts on the Puget Sound ecosystem over the next several decades. These estimates suggest that the role ocean acidification will play in estuaries may be different from the open ocean.

Mixed layer depth variability in the tropical boundary of the California Current, 1997–2007

The variability of the mixed layer depth (MLD) is examined over a decade (1997–2007) for the tropical boundary of the California Current (24–32°N), using conductivity‐temperature‐depth observations collected by quarterly survey cruises. Results indicate that salinity gradients control MLD rather than temperature gradients. The mean state of the upper ocean indicates that contours of constant MLD are parallel to the coast, with mixed layer thickness decreasing toward the coastal zone. The deepest (∼70 m) thickness is reached in January and the shallowest (∼15 m) occurs in July. The warmer conditions (summer) are reproduced for a simple thermal energy equation. The rest of the seasons are reproduced for a one‐dimensional momentum balance for the upper ocean, which includes Ekman dynamics and stratification. This comparison indicates that the variability of MLD is mainly due to wind‐driven phenomena except during the heating period. In particular, seasonal and interannual variability of the MLD are correlated with offshore Ekman transport. An abrupt MLD change occurs between January 1998 and January 2000 associated with the strong El Niño‐La Niña cycle shift that occurred in this period.

Temporal and spatial variations of 137Cs in the waters off a nuclear fuel reprocessing facility in Rokkasho, Aomori, Japan

Five survey cruises were carried out from 2004 to 2007 to determine 137Cs concentrations in the water columns off Rokkasho Village, Aomori Prefecture, Japan, where the spent nuclear fuel reprocessing plant of Japan Nuclear Fuel Ltd has been undergoing test operation since March 2006. Seawater samples were collected with a large volume in situ filtration and concentration system at different depths in the water column. 137Cs in particulate form could not be detected in the survey area. Dissolved 137Cs showed temporal variation, especially in the surface water. Based on the results, it was concluded that no observable 137Cs contamination was present in the investigated area. The distribution of 137Cs concentrations was influenced by the mixing between the Tsugaru and Oyashio Currents.

Upper mixed layer temperature and salinity variability in the tropical boundary of the California Current, 1997–2007

Spatial and temporal interannual variability of mixed layer (ML) temperature and ML salinity off Baja California are examined using empirical orthogonal functions analysis. Conductivity‐temperature‐depth data collected from October 1997 through January 2007 over a grid based on Mexican Research of the California Current quarterly survey cruises are analyzed. Net heat flux (NHF) and sea surface height anomaly (SSH) from satellite products are also analyzed. The first leading mode of both ML temperature and ML salinity show a single‐signed loading pattern, in which the variability increases southward. Those patterns have been reported before, but they are lacking a quantitative explanation. ML temperature variability is mainly associated with NHF variability, while ML salinity variability is mainly associated with large‐scale SSH variability. The principal component (PC) of ML salinity is correlated with North Pacific Gyre Oscillation and Warm Water Volume climate indices, while the PC of ML temperature is only correlated with the latter index. Those results indicate that the principal mode of ML salinity variability is a diagnostic variable of basin‐scale process. An abrupt freshening (∼−0.7) and cooling (∼−4°C) event from January 1998 to January 1999 and an abrupt freshening (∼−0.5) event from January 2002 to January 2003 are conspicuous features in the mixed layer. The 1998–1999 events are associated with the major El Niño–La Niña cycle in the 10‐year period. The 2002–2003 freshening is related to an enhancement of subarctic water into the equatorward flow that started during the summer of 2002 off Oregon (49°N).

Myojin Rift, Izu–Bonin Arc as the Modern Analog of Hokuroku Basin, Northeast Japan: Geotectonic Significance of the New Hydrothermal Deposit in the Back‐Arc Rift

AbstractA huge hydrothermal field, named the “Hakurei Sulfide Deposit” (HSD) was discovered in the North Myojin Rift (NMR), Izu–Bonin Back‐Arc Rift (BAR) during the 2003 survey cruise of R/V Hakurei‐maru No.2. This paper investigates the geotectonic features and the tectonic setting of ore deposits between the NMR and the Hokuroku Basin, which is representative of kuroko fields in Japan. The topographic features of the NMR and the Hokuroku Basin are similar. Both have a clear ring structure surrounded by faults and the east–west width is almost the same. Many kuroko deposits were formed on the extrusion centers of the five pre‐mineral acidic volcanic complexes, located in a loop inside the Hokuroku Basin. In the case of the NMR, seven submarine volcanoes are also located in a loop, and the HSD formed inside the summit caldera of Bayonnaise Knoll, which is one of the seven volcanoes. These topographic similarities highlight that the NMR is a modern analog of the Hokuroku Basin. Identifying such similarities is extremely useful when prospecting kuroko deposits on land equivalents as well as on the other segments of the Izu–Bonin BAR. The probability of finding kuroko deposits on land is expected to increase when the following are identified: (i) location of back‐arc rift and the volcanic front; (ii) direction of the arc–trench system and intra‐rift faults (and/or fracture zone); (iii) position of submarine volcanoes surrounding a back‐arc rift; and (iv) intersections of a caldera fault and intra‐rift fault (and/or fracture zone) inside the summit caldera of submarine volcanoes. Within these aforementioned points a ring structure, acidic volcanic complexes that circle the circuit and submarine calderas along the volcanic front, are an important indication of submarine hydrothermal deposits.

The summertime plankton community at South Georgia (Southern Ocean): Comparing the historical (1926/1927) and modern (post 1995) records

The earliest comprehensive plankton sampling programme in the Southern Ocean was undertaken during the early part of last century by Discovery Investigations to gain a greater scientific understanding of whale stocks and their summer feeding grounds. An initial survey was carried out around South Georgia during December 1926 and January 1927 to describe the distribution of plankton during the summer, and to serve as a baseline against which to compare future surveys. We have reanalysed phytoplankton and zooplankton data from this survey and elucidated patterns of community distribution and compared them with our recent understanding of the ecosystem based on contemporary data. Analysis of Discovery data identified five groups of stations with characteristic phytoplankton communities which were almost entirely consistent with the original analysis conducted by [Hardy A.C., Gunther, E.R., 1935. The plankton of the South Georgia whaling grounds and adjacent waters 1926–1927. Discovery Report 11, 1–456]. Major groupings were located at the western end of the island and over the northern shelf where Corethron spp. were dominant, and to the south and east where a more diverse flora included high abundances of Nitzschia seriata. Major zooplankton-station groupings were located over the inner shelf which was characterised by a high abundance of Drepanopus forcipatus and in oceanic water >500 m deep that were dominated by Foraminifera, Oithona spp., Ctenocalanus vanus, and Calanoides acutus. Stations along the middle and outer shelf regions to the north and west, were characterised by low overall abundance. There was some evidence that groupings of stations to the north of the island originated in different water masses on either side of the Southern Antarctic Circumpolar Current Front, the major frontal system in the deep ocean close to South Georgia. However, transect lines during 1926/1927 did not extend far enough offshore to sample this frontal region adequately. Interannual variability of zooplankton abundance was assessed from stations which were sampled repeatedly during seven recent British Antarctic Survey cruises (1995–2005) to the region and following taxonomic harmonization and numerical standardization (ind. m −3), a subset of 45 taxonomic categories of zooplankton (species and higher taxa) from 1926/1927, were compared with similar data obtained during the BAS cruises using a linear model. Initially comparisons were restricted to BAS stations that lay within 40 km of Discovery stations although a comparison was also made using all available data. Despite low abundance values in 1926/1927, in neither comparison did Discovery data differ significantly from BAS data. Calculation of the percentage similarity index across cruises did not reveal any systematic differences in species composition between 1926 and 1927 and the present. In the light of ocean warming trends, the existence of more subtle changes in species composition is not ruled out, but an absence of finely resolved time-series data make this impossible to determine.

Preliminary observations on the spatial distribution of humpback whales off the north coast of Margarita Island, Venezuela—south-east Caribbean

Megaptera novaeangliae sightings were gathered in the 2002 winter season, between February and April throughout several seismic survey cruises in a study area located north of Margarita Island. The data were processed by GIS (MapInfo 4.5) considering environmental features as underwater topography and bathymetry. The spatial and temporal distribution of M. novaeangliae in the study area suggested a significant concentration of whales within the Margarita – Los Testigos submarine platform region in a transition zone along the shelf edge between the north coast of Margarita Island and la Blanquilla Island. This apparent wintering habitat includes protected calving areas such as the Los Frailes Archipelago and Margarita Island itself. The seasonal presence of this species in the territorial waters of the north-east coast of Venezuela indicates the biological value of these animals, as well as the vulnerability of the whales that dwell in this area to oil and gas exploration and development activities.

Emerging Sensing Technologies For Hydrocarbons and their Potential use as Exploration Devices

Australian waters contain a number of under-explored offshore sedimentary basins, which have or could have significant hydrocarbon accumulations. Current exploration strategies are based primarily upon seismic data acquisition, with other data type acquisition, (e.g. geochemical sampling) requiring further survey cruises. This multiple survey strategy significantly increases exploration costs leading to tough decisions being made upon which surveys to perform when exploration budgets are tight. The attraction of using a single cruise to achieve multiple surveys is therefore of interest in reducing costs and increasing the impact of each exploration dollar.

Nutrient regeneration at bottom after a massive spring bloom in a subarctic coastal environment, Funka Bay, Japan

Nutrient regeneration and oxygen consumption after a spring bloom in Funka Bay were studied on monthly survey cruises from February to November 1998 and from March to December 1999. A high concentration of ammonium (more than 4 µmol l−1) was observed near the bottom (80–90 m) after April. Phosphate and silicate gradually accumulated and dissolved oxygen decreased in the same layer. Salinity near the bottom did not change until summer, leading to the presumption that the system in this layer is semi-closed, so regenerated nutrients were preserved until September. Nitrification due to the oxidation of ammonium to nitrate was observed after June. Nitrite, an intermediate product, was detected at 4–7 µmol L−1 in June and July 1999. Assuming that decomposition is a first order reaction, the rate constant for decomposition of organic nitrogen was determined to be 0.014 and 0.008 d−1 in 1998 and 1999, respectively. The ammonium oxidation rate increased rapidly when the ambient ammonium concentration exceeded 5 µmol L−1. We also performed a budget calculation for the regeneration process. The total amount of N regenerated in the whole water column was 287.4 mmol N m−2 in 4 months, which is equal to 22.8 gC m−2, assuming the Redfield C to N ratio. This is 34% of the primary production during the spring bloom and is comparable to the export production of 25 gC m−2 measured by a sediment trap at 60 m (Miyake et al., 1998).

Air‐sea CO2 fluxes and the continental shelf pump of carbon in the Chukchi Sea adjacent to the Arctic Ocean

The Chukchi Sea, a shallow sea‐ice covered coastal sea adjacent to the Arctic Ocean, exhibits an intense bloom of phytoplankton each year due to the exposure of nutrient‐laden surface waters during the brief summertime retreat and melting of sea‐ice. The impact of phytoplankton production and other factors on the seasonal dynamics of carbon and air‐sea CO2 fluxes were investigated during two survey cruises (5 May–15 June 2002, and 17 July–26 August 2002), as part of the Western Arctic Shelf‐Basins‐Interactions (SBI) project. In springtime, most of the Chukchi Sea was sea‐ice covered (>95%) and remnant winter water was present across the shelf. Surface layer seawater partial pressure of CO2 (pCO2) ranged from ∼200–320 μatm, indicative of undersaturation with respect to atmospheric pCO2, although sea‐ice cover kept rates of air‐to‐sea CO2 flux generally low (<1 mmoles CO2 m2 d−1). By summertime, after sea‐ice retreat, seawater pCO2 contents had decreased to very low values (<80–220 μatm) in response to high rates of localized primary and net community production (NCP) and biological uptake of dissolved inorganic carbon (DIC). In the seasonally sea‐ice free regions of the Chukchi Sea shelf, rates of air‐to‐sea CO2 fluxes, determined using the quadratic wind speed‐transfer velocity relationships of Wanninkhof (1992), were high, ranging from ∼30–90 mmoles CO2 m−2 d−1. In regions of the Chukchi Sea slope (and western Beaufort Sea shelf and Arctic Ocean basin) where sea‐ice cover remained high (>80%), air‐to‐sea CO2 fluxes remained generally low (<2 mmoles CO2 m−2 d−1). Seasonal (i.e., May to September) and annual net air‐to‐sea CO2 fluxes from the Chukchi Sea shelf were estimated at ∼27 ± 7 Tg C yr−1, and 38 ± 7 Tg C yr−1, respectively. The Chukchi Sea represents the largest oceanic CO2 sink in the marginal coastal seas adjacent to the Arctic Ocean. An active continental shelf pump of carbon, driven by the northward transport of nutrient‐rich water of Pacific Ocean origin, high rates of primary and net community production during the sea‐ice free period, and lateral export of organic carbon, maintains the Chukchi Sea shelf and slope as a perennial ocean CO2 sink.

Cross-shore velocity shear, eddies and heterogeneity in water column properties over fringing coral reefs: West Maui, Hawaii

A multi-day hydrographic survey cruise was conducted to acquire spatially extensive, but temporally limited, high-resolution, three-dimensional measurements of currents, temperature, salinity and turbidity off West Maui in the summer of 2003 to better understand coastal dynamics along a complex island shoreline with coral reefs. These data complement long-term, high-resolution tide, wave, current, temperature, salinity and turbidity measurements made at a number of fixed locations in the study area starting in 2001. Analyses of these hydrographic data, in conjunction with numerous field observations, evoke the following conceptual model of water and turbidity flux along West Maui. Wave- and wind-driven flows appear to be the primary control on flow over shallower portions of the reefs while tidal and subtidal currents dominate flow over the outer portions of the reefs and insular shelf. When the direction of these flows counter one another, which is quite common, they cause a zone of cross-shore horizontal shear and often form a front, with turbid, lower-salinity water inshore of the front and clear, higher-salinity water offshore of the front. It is not clear whether these zones of high shear and fronts are the cause or the result of the location of the fore reef, but they appear to be correlated alongshore over relatively large horizontal distances (orders of kilometers). When two flows converge or when a single flow is bathymetrically steered, eddies can be generated that, in the absence of large ocean surface waves, tend to accumulate material. Areas of higher turbidity and lower salinity tend to correlate with regions of poor coral health or the absence of well-developed reefs, suggesting that the oceanographic processes that concentrate and/or transport nutrients, contaminants, low-salinity water or suspended sediment might strongly influence coral reef ecosystem health and sustainability.

Effects of warm water intrusions on populations of macrozooplankton on Georges Bank, Northwest Atlantic

As part of the Georges Bank/North West Atlantic GLOBEC (Global Ocean Ecosystems Dynamics) Program, macrozooplankton and micronekton were collected on 30 Broad Scale Survey Cruises between January–June, 1995–1999, using a 10 m 2 MOCNESS (3 mm mesh). The objective of this study is to examine the effects of warm water intrusions on populations of macrozooplankton, namely Salpa spp., Phronima spp., Neomysis americana, and Crangon septemspinosa, on Georges Bank. Salpa spp. and Phronima spp. showed a large degree of horizontal co-occurrence, being found predominantly in Upper Slope/Gulf Stream Water and Georges Bank/Gulf of Maine Water. Abundances of these taxa showed striking interannual variability, and were only abundant on the southern flank and in the Northeast Channel in late spring/early summer of 1995 and 1999, periods during which AVHRR imagery and hydrographic data showed the presence of warm water intrusions. These intrusions seemed to have little effect on the distribution of other macrozooplankton (e.g., N. americana and C. septemspinosa). Warm water intrusions can directly affect Salpa spp. and Phronima spp. populations by advecting them onto Georges Bank, although other, more resident populations, especially those inside the 100 m isobath, seem to be little affected by such intrusions.

Temporal and spatial distribution of chlorophyll-a in surface waters of the Scotia Sea as determined by both shipboard measurements and satellite data

Abstract Chlorophyll- a (Chl- a ) concentrations in surface waters were measured at 137 hydrographic stations occupied by four research vessels participating in the CCAMLR 2000 Survey and the values were compared to estimates from data acquired by the SeaWiFS satellite. The Chl- a concentrations measured on board ship ranged from 0.06 to 14.6 mg m −3 , a range that includes most surface Chl- a concentrations during mid-summer in the Southern Ocean. Owing to persistent cloud cover over much of the Southern Ocean, it was necessary to acquire multi-day composites of satellite data in order to obtain reliable estimates of Chl- a at each of the hydrographic stations. The correlation between the median value for the eight-day composites and the Chl- a concentrations measured on board ship had an R 2 value of 0.82, with the satellite data under-estimating the values obtained on board ship at high Chl- a concentrations and slightly over-estimating the shipboard data at Chl- a concentrations of −3 . For Chl- a concentrations of −3 , the ratio of the satellite estimates divided by the shipboard values was 0.89 ± 0.45 ( n =50). As the mean Chl- a concentration in most pelagic Antarctic waters is close to 0.5 mg m −3 , satellite estimates for Chl- a concentrations in surface waters are thus close to shipboard measurements, and offer the advantage of providing synoptic maps of Chl- a distribution over extensive areas of the Southern Ocean. Satellite Chl- a images for the months preceding (December 1999) and following (February 2000) the CCAMLR 2000 Survey cruises showed that the general pattern of Chl- a concentration in the Scotia Sea and adjoining waters was similar in all three months, but that the phytoplankton biomass was generally lowest in December, reached maximal values in January, and started to decline in February. In contrast, Chl- a concentrations in Drake Passage declined progressively from early December through February.

A comparative study of Calanus finmarchicus mortality patterns at five localities in the North Atlantic

Abstract We compare the patterns of stage-specific mortality of Calanus finmarchicus at five localities across the North Atlantic Ocean during the spring–summer period of active population growth: Georges Bank, a continental shelf locality in the NW Atlantic, based on 30 broadscale survey cruises in the US GLOBEC program; the northern North Sea, studied during the historic FLEX program with sampling four times daily for 73 days; Ocean Station M in the central Norwegian Sea, based on an 80-day daily time-series; and Lurefjorden (sampled weekly in late winter–early summer) and Sørfjorden (sampled monthly), two fjords in southwestern Norway characterized by markedly different guilds of predators. The mortality estimation methods included Wood's Population Surface Method, the Vertical Life Table (VLT) method, and a modified VLT, according to the study site and copepod recruitment schedules. Contrary to assumptions implicit in many simulation models and indirect methods for estimating zooplankton mortality, both rates and stage-specific patterns of mortality of C. finmarchicus vary appreciably across the North Atlantic. Characteristics of local environments, including the predator field in particular, appear to strongly influence mortality schedules in different regions. In at least two sites (Georges Bank and Ocean Station M), mortality rates of early stages of C. finmarchicus are density-dependent. We attribute this density-dependent mortality to egg cannibalism, which introduces non-linear population responses to changing environmental conditions. Region-specific biological interactions can substantially modify the effects of physical climate variability and render simple linear relationships between climate and zooplankton abundance unlikely.

Springtime nutrient and phytoplankton dynamics on Georges Bank

The dynamics of phytoplankton and nutrients before, during and after the winter-spring bloom on Georges Bank were studied on 6 monthly survey cruises from January to June 1999. We measured hydrography, phytoplankton cell densities, chlorophyll a, dissolved inorganic nutrients (NO3 + NO2, NH4, Si(OH)4, PO4), dissolved organic nitrogen (DON) and phosphorus (DOP), particu- late organic carbon (POC) and nitrogen (PON) and total particulate phosphorus (TPP). We present evidence that phytoplankton production may be significant year-round, and that the winter-spring bloom may have started in January. From January to April the phytoplankton was comprised almost exclusively of diatoms, reaching cell densities in March and April of ca. 450 cells ml -1 ; chlorophyll a concentrations exceeded 10 µg l -1 in April. Diatoms decreased to relatively low levels in May ( 300 × 10 3 cells l -1 ). Densities of dinoflagellates and nanoflagellates were low ( 15 µg l -1 in June. Overall micro-and nanoplankton biomass, measured as POC, PON and TPP, increased over the 6 mo period, as did nutritional quality of that biomass as indicated by declining C:N ratios. Our results suggest there may have been an increase in the het- erotrophic component of the plankton in May and June which coincided with a second burst in diatom abundance. We discuss general features of planktonic production and nutrient dynamics with respect to year-round production on the Bank.

Distribution and air-water exchange of carbon dioxide in the Scheldt plume off the Belgian coast

In the present paper we report partial pressure of CO2 (pCO2) data obtained off the Belgian coast during 24 cruises. The temporal and spatial resolution of this data set allows us to discuss satisfactorily seasonal and inter-annual variability of pCO2 in the study area. The dynamics of pCO2 are described using two approaches: fixed reference stations and area survey cruises. The air-water fluxes of CO2 in the Scheldt estuarine plume and in the outer- plume region are estimated quantitatively, showing that these areas correspond respectively to a net annual source and sink of atmospheric CO2. The annually integrated air-water fluxes for the Scheldt estuarine plume range between +1.1 and +1.9 mol m −2 year −1 as a function of the formulation of the exchange coefficient of CO2. The annual net emission of CO2 from the estuarine plume to the atmosphere is estimated to be between +2.3 to +4.0 Gmol year −1 which represents 17 to 29% of the estimate reported in the literature for the Scheldt inner estuary.

South Atlantic and North Atlantic geomagnetic paleointensity stacks (0–80 ka): implications for inter-hemispheric correlation

Recent coring of high-deposition-rate Atlantic sediments has led to the development of North Atlantic (NAPIS) and South Atlantic (SAPIS) geomagnetic paleointensity stacks. The SAPIS stack comprises five records from the sub-Antarctic South Atlantic (41–47°S, 6–10°E). Four are from piston cores collected during the Ocean Drilling Program (ODP) Leg 177 site survey cruise (Earth Planet. Sci. Lett. 175 (2000) 145). The other is ODP Site 1089 (Leg 177) (J. Geophys. Res., 2001, submitted for publication). All but one (4-PC03) of the SAPIS cores have oxygen isotope records which are used in conjunction with lithologic and geomagnetic variability to derive an optimized correlation to Site 1089. The Site 1089 age model is derived by mapping the benthic and planktic isotope data to those from nearby core RC11-83 which has 14 calibrated radiocarbon ages in the 11–41 ka interval. Below this level, the chronology is derived by matching the Site 1089 benthic oxygen isotope data to the SPECMAP stack. The NAPIS stack comprises six records from a wide area of the North Atlantic (Philos. Trans. R. Soc. Ser. A 358 (2000) 1009). Correlation between cores was based on marine isotopic stage boundaries, augmented by millennial-scale features (Heinrich events and fluctuations in concentration-dependent magnetic parameters). NAPIS was placed on the GISP2 chronology, using the marine to ice-core oxygen isotope correlation proposed by Voelker et al. (Radiocarbon 40 (1998) 517) for one of the NAPIS cores. In the resulting age model, the Laschamp Event, recorded in five of six cores, falls in a very narrow (<1 kyr) age range and coincides with the 10Be and 36Cl peak measured in the ice cores. Comparison of the two stacks, placed on their own independent age models, indicates that common millennial scale paleointensity features are preserved. Although more work is needed to define the “true” global content of the paleointensity record as well as the precise age of many features, it is readily apparent that paleointensity can provide a global correlation tool at a resolution unattainable from isotope data alone.

Seasonal CO2 fluxes in the tropical and subtropical Indian Ocean

Abstract Improved estimates of the variability in air–sea CO2 fluxes on seasonal and interannual time scales are necessary to help constrain the net partitioning of CO2 between the atmosphere, oceans and terrestrial biosphere. Few direct measurements of the carbon system have been made in the main Indian Ocean basin. In the mid 1990s, several global carbon measurement programs focused on the Indian Ocean, greatly increasing the existing carbon database for this basin. This study examines the combined surface CO2 measurements from three major US programs in the Indian Ocean: the global carbon survey cruises, conducted in conjunction with the World Ocean Circulation Experiment (WOCE), the NOAA Ocean-Atmosphere Carbon Exchange Study (OACES) Indian Ocean survey and the Joint Global Ocean Flux Study (JGOFS) Arabian Sea Process Study. These data are fit with multiparameter linear regressions as a function of commonly measured hydrographic parameters. These fits are then used with NCEP/NCAR reanalysis and Levitus 94 gridded values to evaluate the seasonal variability of surface seawater CO2 in the tropical and subtropical Indian Ocean and to estimate the magnitude of the Indian Ocean as a net sink for atmospheric CO2. The net annual flux for the Indian Ocean (north of 36°S) was −12.4±0.5×1012 mol of carbon (equivalent to −0.15 Pg C) in 1995. The relatively small net flux results from the very different surface water pCO2 distributions and seasonal variations in the northern and southern Indian Ocean. The equatorial and northern hemisphere regions have values that are generally above atmospheric values. During the S-W monsoon, pCO2 values in the Arabian Sea coastal upwelling region are among the highest observed in the oceans. The upwelling is seasonal in nature, however, and only affects a relatively small area. The Indian Ocean equatorial region generally has values slightly above atmospheric. Unlike the Pacific and Atlantic Oceans, however, no clear equatorial upwelling signature was observed in 1995. The Southern Hemisphere Indian Ocean, which represents the largest region by area, generally has values below atmospheric. The strongest undersaturations are observed in the austral winter, with summer values reaching near or slightly above atmospheric.