A major term in the global carbon cycle is the ocean's biological carbon pump which is dominated by sinking of small organic particles from the surface ocean to its interior. Several different approaches to estimating the magnitude of the pump have been used, yielding a large range of estimates. Here, we use an alternative methodology, a thorium isotope tracer, that provides direct estimates of particulate organic carbon export. A large database of thorium‐derived export measurements was compiled and extrapolated to the global scale by correlation with satellite sea surface temperature fields. Our estimates of export efficiency are significantly lower than those derived from the f‐ratio, and we estimate global integrated carbon export as ∼5 GtC yr−1, lower than most current estimates. The lack of consensus amongst different methodologies on the strength of the biological carbon pump emphasises that our knowledge of a major planetary carbon flux remains incomplete.

The Atlantic Ocean receives warm, saline water from the Indo-Pacific Ocean through Agulhas leakage around the southern tip of Africa. Recent findings suggest that Agulhas leakage is a crucial component of the climate system and that ongoing increases in leakage under anthropogenic warming could strengthen the Atlantic overturning circulation at a time when warming and accelerated meltwater input in the North Atlantic is predicted to weaken it. Yet in comparison with processes in the North Atlantic, the overall Agulhas system is largely overlooked as a potential climate trigger or feedback mechanism. Detailed modelling experiments--backed by palaeoceanographic and sustained modern observations--are required to establish firmly the role of the Agulhas system in a warming climate.

Abstract. Ice-edge blooms are significant features of Arctic primary production, yet have received relatively little attention. Here we combine satellite ocean colour and sea-ice data in a pan-Arctic study. Ice-edge blooms occur in all seasonally ice-covered areas and from spring to late summer, being observed in 77-89% of locations for which adequate data exist, and usually peaking within 20 days of ice retreat. They sometimes form long belts along the ice-edge (greater than 100 km), although smaller structures were also found. The bloom peak is on average more than 1 mg m −3 , with major blooms more than 10 mg m −3 , and is usually located close to the ice-edge, though not always. Some propagate behind the receding ice-edge over hundreds of kilometres and over several months, while others remain stationary. The strong connection between ice retreat and productivity suggests that the ongoing changes in Arctic sea-ice may have a significant impact on higher trophic levels and local fish stocks.

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Measurements of primary production (PP), calcification (CF), and coccolithophore abundance were made during late summer (July-August 2007) in the Iceland Basin. Low numbers of coccolithophore cells and detached coccoliths (, 1 3 10 3 cells mL 21 and 1-15 3 10 3 coccoliths mL 21 , respectively) indicated a non-bloom community, with Emiliania huxleyi as the dominant coccolithophore in terms of abundance, coccolithophore organic biomass, and cell calcite. PP ranged from 0.1 to 2 mmol C m 23 d 21 , while CF ranged from 10 to 250 mmol C m 23 d 21 , with both typically decreasing with depth. Coccolithophores were estimated to contribute 10-20% toward total chlorophyll a, phytoplankton carbon, and PP within the euphotic zone. In these non-bloom conditions, , 30-60% of the total calcite in the water column was present as detached coccoliths rather than whole cells. Both cell numbers and variability in cell-normalized CF controlled the magnitude of total CF, and hence both physiological limits to cell CF and growth, as well as mortality factors, need to be taken into account when examining oceanic coccolithophore communities. Combining cell-normalized CF with an estimate of coccolith calcite gave coccolith production rates (0.4-1.8 h 21 ) similar to those reported in the literature for laboratory cultures of E. huxleyi. None of the factors currently associated with coccolithophore blooms (irradiance, mixed-layer depth, nitrate, phosphate, or calcite saturation) showed a clear correlation with community or cellular CF. Hence, although mortality is likely to control cell numbers, other factors such as trace metal (iron) availability may influence coccolithophore physiology in the central Iceland Basin during late summer.Late-summer satellite images from high-latitude temperate seas, such as the Iceland Basin and Patagonian Shelf, often show large-scale patches of highly reflective water (Brown and Yoder 1994). These striking features are coccolithophore blooms , often dominated by Emiliania huxleyi, although other species (e.g., Coccolithus pelagicus, Gephyrocapsa spp.) are usually present at low relative densities . The high reflective index of these blooms is caused by the shedding of coccoliths (Holligan et al. 1983;Balch et al. 1999): calcite plates that coccolithophores use to form a composite exoskeleton, the coccosphere. Coccoliths are detached from the coccosphere by both healthy and environmentally stressed cells, with detachment rates low during steady-state growth and increasing sharply under nutrient stress (Balch et al. 1993(Balch et al. , 1996. In the case of coccolithophore blooms, the white waters detected by satellites are caused by detached coccoliths rather than by cells (Balch et al. 1999), when nutrient concentrations are depleted, rates of primary production (PP) and calcification (CF) are unbalanced, and the coccolithophore community is in decline Holligan et al. 1993).The factors favoring the formation of coccolithophore blooms, defined as large patches of high-reflectance water in satellit...

Sea state information is needed for many applications, ranging from safety at sea and on the coast, for which real time data are essential, to planning and design needs for infrastructure that require long time series. The definition of the wave climate and its possible evolution requires high resolution data, and knowledge on possible drift in the observing system. Sea state is also an important climate variable that enters in air-sea fluxes parameterizations. Finally, sea state patterns can reveal the intensity of storms and associated climate patterns at large scales, and the intensity of currents at small scales. A synthesis of user requirements leads to requests for spatial resolution at kilometer scales, and estimations of trends of a few centimeters per decade. Such requirements cannot be met by observations alone in the foreseeable future, and numerical wave models can be combined with in situ and remote sensing data to achieve the required resolution. As today's models are far from perfect, observations are critical in providing forcing data, namely winds, currents and ice, and validation data, in particular for frequency and direction information, and extreme wave heights. In situ and satellite observations are particularly critical for the correction and calibration of significant wave heights to ensure the stability of model time series. A number of developments are underway for extending the capabilities of satellites and in situ observing systems. These include the generalization of directional measurements, an easier exchange of moored buoy data, the measurement of waves on drifting buoys, the evolution of satellite altimeter technology, and the measurement of directional wave spectra from satellite radar instruments. For each of these observing systems, the stability of the data is a very important issue. The combination of the different data sources, including numerical models, can help better fulfill the needs of users.

The Agulhas Current with its retroflection and attendant eddy-shedding is the cause of some of the greatest mesoscale variability in the ocean. This paper considers the area to the south and east of Madagascar, which provides some of the source waters of the Agulhas Current, and examines the propagating sea surface height signals in altimetry and output from a numerical model, OCCAM. Both show bands of variability along the axis of the East Madagascar Current (EMC) and along a zonal band near 25˚S. Sequences of images plus associated temperature data suggest that a number of westward-propagating eddies are present in this zonal band. The paper then focuses on the region to the south of the island, where ocean colour and infra-red imagery are evocative of an East Madagascar Retroflection. The synthesis of data analysed in this paper, however, show that remotely observed features in this area can be explained by anticyclonic eddies moving westward through the region, and this explanation is consistent with numerical model output and the trajectories of drifting buoys.

The Agulhas Current system contains one of the world's strongest western boundary currents, and plays an important part in the warm water path of the global thermohaline circulation. However, there have been few surveys of the source regions of the Agulhas Current, and thus little in situ measurement of their variability. Utilizing the more than 5-year record of SeaWiFS data, we examine the eddy activity present in the southern portion of the Mozambique Channel. The two sources of Agulhas input from the central Indian Ocean (southward flow through the Mozambique Channel and westward flow around the southern limit of Madagascar) both show great temporal variability, with no clear seasonal signal. A number of large (-200 km diameter) anticyclonic rings intermittently propagate poleward along the western edge of the channel, sweeping coastal waters into mid channel. Their passage past Maputo appears to affect the circulation of the lee eddy in the Delagoa Bight. The eastern side of the channel is mainly characterized by cyclonic eddies. These are made manifest in the lee of the southern tip of Madagascar, although it is not clear whether many form there or just develop a visible presence due to entrainment of high chlorophyll coastal waters. Several of these cyclonic eddies then appear to move in west-southwesterly direction. The chlorophyll data do reveal the East Madagascar retroflection on occasions, but do not show clear examples of the pinching off of anticyclonic eddies. However surface waters from the East Madagascar Current may reach the African mainland on occasions when no retroflection is present.