Distribution and transport of organic matter along a filament-eddy system in the Canaries – NW Africa coastal transition zone region

The distribution and transport of chlorophyll a (Chla), particulate (POC) and dissolved (DOC) organic carbon, and the respiratory ETS activity of the microplankton community were studied along a filament-eddy system located in the transition zone between the NW Africa upwelling and Canary Islands waters. Two independent filaments (F1 and F2) stemming from the coastal jet, between Cape Juby and Cape Bojador, merged about 100 km offshore, turning southward and onshore forced by the circulation of a recurrent oceanic cyclonic eddy. In general, the coastal upwelling waters presented higher Chla, but lower POC, DOC and ETS activity than filament waters. However, differences in organic carbon distribution and respiratory activity were observed among stations from the two filaments. The bio-chemical fields were strongly influenced by a complex sub-mesoscale hydrography resulting from the interaction of cyclonic and anticyclonic island eddies with the filaments. The combined F1 + F2 filament system transported 97.1 kg s⁻¹ of excess (non-refractory) total organic carbon (e-TOC), a value comparable to other published estimates from upwelling filaments in the NE Atlantic. About 90% of e-TOC was exported as DOC, since eddy re-circulation precluded the offshore transport of POC. Assuming that the calculated transport of e-TOC is representative of the annual average, the yearly offshore transport (3.1 x 10⁹ kg C) would represent about 25% of the upwelling primary production of the region of study.     

Wind-driven interannual variability over the northeast Pacific Ocean

Interannual variability of the sea surface height (SSH) over the northeast Pacific Ocean is hindcast with a reduced-gravity, quasi-geostrophic model that includes linear damping. The model is forced with monthly Ekman pumping fields derived from the NCEP reanalysis wind stresses. The numerical solution is compared with SSH observations derived from satellite altimeter data and gridded at a lateral resolution of 1 degree. Provided that the reduced gravity parameter is chosen appropriately, the results demonstrate that the model has significant hindcast skill over interior regions of the basin, away from continental boundaries. A damping time scale of 2 to 3 years is close to optimal, although the hindcast skill is not strongly dependent on this parameter.A simplification of the quasi-geostrophic model is considered in which Rossby waves are eliminated, yielding a Markov model driven by local Ekman pumping. The results approximately reproduce the hindcast skill of the more complete quasi-geostrophic model and indicate that the interannual SSH variability is dominated by the local response to wind forcing. There is a close correspondence the two leading empirical orthogonal modes of the local model and those of the observed SSH anomalies. The latter account for over half of the variance of the interannual signal over the region.     

Mesopelagic fishes of the Bering Sea and adjacent northern North Pacific Ocean

Fourteen midwater trawl collections to depths of 450 m to 1,400 m were taken at eleven stations in the Bering Sea and adjoining regions of the northern North Pacific by the R/V Hakuho Maru during the summer of 1975. A total of 29 kinds of fishes were identified. Mesopelagic fishes of the families Myctophidae, Gonostomatidae and Bathylagidae predominated in the catches, contributing 14 species (94%) of the fishes caught.Seventeen species of fishes were caught in the Bering Sea, and all of these are known from nearby areas. The mesopelagic fish fauna of the Bering Sea is similar to that in adjoining regions of the northern North Pacific Ocean: endemic species are rare or absent. Stenobrachius nannochir was usually the most common mesopelagic fish in our catches.Stenobrachius leucopsarus is a diel vertical migrant that is usually the dominant mesopelagic fish in modified Subarctic waters of the northeastern Pacific. The change in dominance fromS. nannochir in the western Bering Sea toS. leucopsarus in the eastern Bering Sea is related to differences in oceanographic conditions.     

Offshore permafrost and gas hydrate stability zone on the shelf of East Siberian Seas

Dynamics of the submarine permafrost regime, including distribution, thickness, and temporal evolution, was modeled for the Laptev and East Siberian Sea shelf zones. This work included simulation of the permafrost-related gas hydrate stability zone (GHSZ). Simulations were compared with field observations. Model sensitivity runs were performed using different boundary conditions, including a variety of geological conditions as well as two distinct geothermal heat flows (45 and 70 mW/m²). The heat flows used are typical for the coastal lowlands of the Laptev Sea and East Siberian Sea. Use of two different geological deposits, that is, unconsolidated Cainozoic strata and solid bedrock, resulted in the significantly different magnitudes of permafrost thickness, a result of their different physical and thermal properties. Both parameters, the thickness of the submarine permafrost on the shelf and the related development of the GHSZ, were simulated for the last four glacial-eustatic cycles (400,000 years). The results show that the most recently formed permafrost is continuous to the 60-m isobath; at the greater depths of the outer part of the shelf it changes to discontinuous and patchy permafrost. However, model results suggest that the entire Arctic shelf is underlain by relic permafrost in a state stable enough for gas hydrates. Permafrost, as well as the GHSZ, is currently storing probable significant greenhouse gas sources, especially methane that has formed by the decomposition of gas hydrates at greater depth. During climate cooling and associated marine regression, permafrost aggradation takes place due to the low temperatures and the direct exposure of the shelf to the atmosphere. Permafrost degradation takes place during climate warming and marine transgression. However, the temperature of transgressing seawater in contact with the former terrestrial permafrost landscape remains below zero, ranging from –0.5 to –1.8°C, meaning permafrost degradation does not immediately occur. The submerged permafrost degrades slowly, undergoing a transformation in form from ice bonded terrestrial permafrost to ice bearing submarine permafrost that does not possess a temperature gradient. Finally the thickness of ice bearing permafrost decreases from its lower boundary due to the geothermal heat flow. The modeling indicated several other features. There exists a time lag between extreme states in climatic forcing and associated extreme states of permafrost thickness. For example, permafrost continued to degrade for up to 10,000 years following a temperature decline had begun after a climate optimum. Another result showed that the dynamic of permafrost thickness and the variation of the GHSZ are similar but not identical. For example, it can be shown that in recent time permafrost degradation has taken place at the outer part of the shelf whereas the GHSZ is stable or even thickening.     

Variations of antioxidant efficiency and presence of endosymbiotic diatoms in the Antarctic porifera Haliclona dancoi

The role of endosymbiotic diatoms as pro-oxidant stressors in porifera has been investigated in the Antarctic sponge Haliclona dancoi in which the presence of diatoms is influenced by marked seasonal variations during the austral summer. Both chlorophaeopigments and frustules were absent in sponge tissues sampled in early November at the beginning of the summer and increased from the mid of December with slightly shifted temporal trends. The efficiency of antioxidant defenses in the sponge showed a marked response to symbionts with clearly enhanced values corresponding to the peak of diatoms.     

Meanders in the Antarctic Polar Frontal Zone and their impact on phytoplankton

The Antarctic Polar Front is a complex set of meandering jets, which appear to support enhanced primary productivity. The US Joint Global Ocean Flux Study conducted a series of survey and process studies in part to study the processes regulating primary productivity in this high nutrient, low chlorophyll region. We deployed a set of surface velocity drifters, some of which were equipped with bio-optical sensors, to study the temporal and spatial scales of biological and physical processes in the Antarctic Polar Frontal Zone. There were two primary sets of deployments: November 1997 before the spring bloom and January 1998 after the spring bloom. The November deployment revealed a strong spring bloom that lasted about 10 days. In late spring, when incoming solar radiation began to increase, the vertical motions associated with the meanders strongly affected the accumulation of phytoplankton biomass, primarily through their impact on light availability. Weaker meandering was observed in the January deployment, and chlorophyll values remained relatively constant. As the bloom began to decay, it appears that nutrient availability became more important in regulating phytoplankton photosynthesis. Some of the drifters in the November deployment were deployed in coherent clusters, thus allowing us to calculate vertical velocities associated with the meanders. Estimates of fluorescence/chlorophyll suggest that areas of upwelling and downwelling alternately decrease and increase photosynthetic stress, perhaps as a result of changes in the availability of iron or light during the formation of the bloom.