Is there a connection between high transport of water through the Rockall Trough and ecological changes in the North Sea?

Changes in the ecosystem of the North Sea may occur as pronounced inter-annual and step-wise shifts as well as gradual trends. Marked inter-annual shifts have occurred at least twice in the last two decades, the late 1980s and the late 1990s, that appear to reflect an increased inflow of oceanic water and species. Numerical modelling has demonstrated a link between altered rates of inflow of oceanic water into the northern North Sea and a regime shift after 1988. In 1989 and 1997 oceanic species not normally found in the North Sea were observed there, suggesting pulses of oceanic water had entered the basin and triggered the subsequent ecosystem change. The oceanic water has origins mainly west of Britain in the Rockall Trough, where the long-term mean volume transport is around 3.7Sv northwards (1Sv=10 super(6)m super(3)s super(1)), but in early 1989 and early 1998 was observed to be more than twice the mean value, reaching over 7Sv. These periods of high transport coinciding with the inferred pulses of oceanic water into the North Sea suggest a connection through the continental shelf edge current. Copyright 2001 International Council for the Exploration of the Sea

Seasonal-Changes In The Physiology Reproductive Condition And Carbohydrate Content Of The Cockle Cardium (=Cerastoderma) Edule (Bivalvia Cardiidae)

Pronounced seasonal cycles in the rates of oxygen consumption and feeding were found for Cardium (=Cerastoderma) edule L. measured in the field under ambient conditions. The cockles had a maximum rate of oxygen consumption (0.89 ml O2 g-1 h-1) in April which declined to a minimum of 0.35 ml O2 g-1 h-1 in March. Their feeding rate was variable but had a maximum value (3.91 l g-1 h-1) in April and a minimum value (0.73 l g-1 h-1) in October. There was no apparent seasonal variation in absorption efficiency, with a mean value of 67.6%. Gametogenesis was initiated in January and the population reached a peak in reproductive condition in April/May, followed by a 3 month spawning period. Carbohydrate reserves were synthesised during spawning, and were then utilised during the winter and early spring. An adaptive function for a reduction in time spent feeding is postulated, and correlations between the rates of certain physiological processes and some exogenous and endogenous variables are discussed.

Coccolithophore surface distributions in the North Atlantic and their modulation of the air-sea flux of CO2 from 10 years of satellite Earth observation data

Coccolithophores are the primary oceanic phytoplankton responsible for the production of calcium carbonate (CaCO3). These climatically important plankton play a key role in the oceanic carbon cycle as a major contributor of carbon to the open ocean carbonate pump (similar to 50 %) and their calcification can affect the atmosphere-to-ocean (air-sea) uptake of carbon dioxide (CO2) through increasing the seawater partial pressure of CO2 (pCO(2)). Here we document variations in the areal extent of surface blooms of the globally important coccolithophore, Emiliania huxleyi, in the North Atlantic over a 10-year period (1998-2007), using Earth observation data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). We calculate the annual mean sea surface areal coverage of E. huxleyi in the North Atlantic to be 474 000 +/- 104 000 km(2), which results in a net CaCO3 carbon (CaCO3-C) production of 0.14-1.71 Tg CaCO3-C per year. However, this surface coverage (and, thus, net production) can fluctuate inter-annually by -54/+81% about the mean value and is strongly correlated with the El Nino/Southern Oscillation (ENSO) climate oscillation index (r = 0.75, p < 0.02). Our analysis evaluates the spatial extent over which the E. huxleyi blooms in the North Atlantic can increase the pCO(2) and, thus, decrease the localised air-sea flux of atmospheric CO2. In regions where the blooms are prevalent, the average reduction in the monthly air-sea CO2 flux can reach 55%. The maximum reduction of the monthly air-sea CO2 flux in the time series is 155 %. This work suggests that the high variability, frequency and distribution of these calcifying plankton and their impact on pCO(2) should be considered if we are to fully understand the variability of the North Atlantic air-to-sea flux of CO2. We estimate that these blooms can reduce the annual N. Atlantic net sink atmospheric CO2 by between 3-28 %.

The origin of sub-surface source waters define the sea-air flux of methane in the Mauritanian Upwelling, NW Africa

Concentrations and flux densities of methane were determined during a lagrangian study of an advective filament in the permanent upwelling region off western Mauritania. Newly upwelled waters were dominated by the presence of North Atlantic Central Water and surface CH4 concentrations of 2.2 ± 0.3 nmol L-1 were largely in equilibrium with atmospheric values, with surface saturations of 101.7 ± 14%. As the upwelling filament aged and was advected offshore, CH4 enriched South Atlantic Central Water from intermediate depths of 100 to 350m was entrained into the surface mixed layer of the filament following intense mixing associated with the shelf break. Surface saturations increased to 198.9 ± 15% and flux densities increased from a mean value over the shelf of 2.0 ± 1.1 µmol m-2d-1 to a maximum of 22.6 µmol m-2d-1. Annual CH4 emissions for this persistent filament were estimated at 0.77 ± 0.64 Gg which equates to a maximum of 0.35% of the global oceanic budget. This raises the known outgassing intensity of this area and highlights the importance of advecting filaments from upwelling waters as efficient vehicles for air-sea exchange.