Shell architecture,element composition,and stable isotope signature of the giant deep-sea oyster Neopycnodonte zibrowii sp. n. from the NE Atlantic

A conspicuous new deep-sea oyster, Neopycnodonte zibrowii sp. n., is described from the Azores Archipelago, where it thrives in 420 to >500 m water depth in high densities concealed underneath overhangs. The new species reaches a relatively large size, which may exceed 20 cm, and is characterised by a very unusual hinge line morphology, straight without a bulge of the resilium. It is compared to the extant Indo-Pacific Empressostrea kostini Huber and Lorenz, 2007 and to the cosmopolitan Neopycnodonte cochlear (Poli, 1791), which has a broadly sympatric distribution at shallower depths in the Azores and Bay of Biscay. Radiocarbon dating reveals that individuals reach an impressive lifespan of one to more than five centuries, placing them among the longest-lived molluscs known to date. They often grow on top of each other, forming stacks that resemble dish piles—an effective measure to optimise shell stability with minimal biomineralisation effort, but with the drawback of increased bioerosion ultimately leading to detachment.Three microstructure types are developed in N. zibrowii: (1) the cross-foliated, calcitic, dorsal to central endostracum and aragonitic ligostracum, (2) the porous vesicular structure of the calcitic ventral endostracum, and (3) the simple prismatic aragonitic myostracum. Foliated and vesicular shell portions show sub-millimetre-scale first-order increments delineated by conchiolin-rich growth breaks (interpreted as reproductive cyclicity), and less distinct second-order increments (interpreted as annual in nature). This pattern is clearly reflected by the elemental composition with the primary growth breaks lacking Ca and Sr but including Mg and S as organic matrix constituents. The second-order increments within the calcite are mirrored by moderately co-varying Mg/Ca and S/Ca fluctuations at stable Sr concentrations, reflecting varying proportions of organic matrix. Dorsal and central endostracum transects reveal a low inter-valve, but considerable inter-specimen variability with high Mg/Ca molar ratios and fluctuations (22.5±17.6 mmol/mol), low Sr/Ca values (0.2±0.1 mmol/mol), and a typical to high S/Ca content (6.9±2.2 mmol/mol), when compared to other calcitic bivalves.Unlike short-lived, shallow-water oysters, N. zibrowii thrives under very stable environmental conditions. Minimal temperature fluctuations and stable open marine salinity provide an optimal basis to recognise biological fractionation processes. Strong Mg/Ca fluctuations indicate a physiological control related to metabolism and biomineralisation, prohibiting the use of this ratio as a temperature or ocean chemistry proxy. Low Sr/Ca ratios indicate rather constant and low long-term accretion rates, while short-scale fluctuations may be attributed to short-term variations in growth rate and Mg incorporation. Oxygen isotopes yield a considerable spread of 1.8‰ with a mean of 2.0±0.3‰ δ¹⁸O V-PDB, and low correlation between different contemporaneous parts of the shell and between specimens. These values surprisingly exceed expected equilibrium conditions, calculated from in situ temperature data (annual mean 12.3±0.3 °C) and seawater isotopic composition (0.5±0.1‰ δ¹⁸O SMOW), by 0.5‰ on average. Such positively shifting vital effects, previously reported for limpets and barnacles, are often overlooked in high-temperature and high-amplitude settings and may be more common than is currently believed. Carbon isotopes range from 0.2 to 3.5‰ δ¹³C V-PDB (mean 1.8±0.7‰) and show an ontogenetic decrease, but may incorporate an environmental signal in adult portions, indicated by a strong correspondence of peaks between specimens. This signal is likely driven by a complex interplay of different factors, such as primary production, current-based food supply and metabolism.     

Short-term environmental variability in cold-water coral habitat at Viosca Knoll,Gulf of Mexico

The Lophelia pertusa community at Viosca Knoll (VK826) is the most extensive found to date in the Gulf of Mexico. As part of a multi-disciplinary study, the physical setting of this area was described using benthic landers, CTD transects and remotely operated vehicle observations. The site was broadly characterised into three main habitats: (1) dense coral cover that resembles biogenic reef complexes, (2) areas of sediment, and (3) authigenic carbonate blocks with sparse coral and chemosynthetic communities. The coral communities were dominated by L. pertusa but also contained numerous solitary coral species. Over areas that contained L. pertusa, the environmental conditions recorded were similar to those associated with communities in the north-eastern Atlantic, with temperature (8.5–10.6 °C) and salinity (～35) falling within the known species niche for L. pertusa. However, dissolved oxygen concentrations (2.7–2.8 ml l^?1) and density (σ_Θ, 27.1–27.2 kg m^?3) were lower and mass fluxes from sediment trap data appeared much higher (4002–4192 mg m^?2 d^?1). Yet, this species still appears to thrive in this region, suggesting that L. pertusa may not be as limited by lower dissolved oxygen concentrations as previously thought. The VK826 site experienced sustained eastward water flow of 10–30 cm s^?1 over the 5-day measurement period but was also subjected to significant short-term variability in current velocity and direction. In addition, two processes were observed that caused variability in salinity and temperature; the first was consistent with internal waves that caused temperature variations of 0.8 °C over 5–11 h periods. The second was high-frequency variability (20–30 min periods) in temperature recorded only at the ALBEX site. A further pattern observed over the coral habitat was the presence of a 24 h diel vertical migration of zooplankton that may form part of a food chain that eventually reaches the corals. The majority of detailed studies concerning local environmental conditions in L. pertusa habitats have been conducted within the north-eastern Atlantic, limiting most knowledge of the niche of this species to a single part of an ocean basin. Data presented here show that the corals at VK826 are subjected to similar conditions in temperature, salinity, and flow velocity as their counterparts in the north-east Atlantic, although values for dissolved oxygen and density (sigma-theta: σ_Θ) are different. Our data also highlight novel observations of short-term environmental variability in cold-water coral habitat.     

Florida Current transport variability: An analysis of annual and longer-period signals

More than forty years of Florida Current transport estimates are combined to study annual and longer-term variability in this important component of the MOC and subtropical gyre. A detailed analysis with error estimates illustrates the difficulties in extracting annual and longer time scale variability given the strong higher frequency energy present. The annual cycle represents less than 10% of the total Florida Current transport variance in a 16 yr segment of the record, while interannual (13–42 month) variability represents only 13% of the total and periods longer than 42 months represents less than 10% of the total. Given the observed high frequency variability of the Florida Current, in order to get a monthly mean that is accurate to within 0.5 Sv (one standard error level) more than 20 daily observations are needed. To obtain an estimate of the annual climatology that is “accurate” to within 20% of its own standard deviation, at least 24 yr of data is needed. More than 40 observations spread throughout a year are required to obtain an annual mean that is accurate to within 0.5 Sv. Despite these daunting data requirements, there is sufficient data now to evaluate both the annual cycle of the Florida Current transport with a high degree of accuracy and to begin to determine the longer period transport variability. Comparison of the Florida Current, NAO and wind stress curl records shows that a recently described Sverdrup-based mechanism explains a significant fraction of the long-period variability primarily during the 1986–1998 time window, with other mechanisms clearly dominating before and after.     

The annual cycle of vertical mixing and restratification in the Northern Gulf of Eilat/Aqaba (Red Sea) based on high temporal and vertical resolution observations

The stratification in the Northern Gulf of Eilat/Aqaba follows a well-known annual cycle of well-mixed conditions in winter, surface warming in spring and summer, maximum vertical temperature gradient in late summer, and erosion of stratification in fall. The strength and structure of the stratification influences the diverse coral reef ecosystem and also affects the strength of the semi-diurnal tidal currents. Long-term (13 months) moored thermistor data, combined with high temporal and vertical resolution density profiles in deep water, show that transitions from summer to fall and winter to spring/summer occur in unpredictable, pulses and are not slow and gradual, as previously deduced from monthly hydrographic measurements and numerical simulations forced by monthly climatologies. The cooling and deepening of the surface layer in fall is marked by a transition to large amplitude, semi-diurnal isotherm displacements in the stratified intermediate layer. Stratification is rebuilt in spring and summer by intermittent pulses of warm, buoyant water that can increase the upper 100–150 m by 2 °C that force surface waters down 100–150 m over a matter of days. The stratification also varies in response to short-lived eddies and diurnal motions during winter. Thus, the variability in the stratification exhibits strong depth and seasonal dependence and occurs over range of timescales: from tidal to seasonal. We show that monthly or weekly single-cast hydrographic data under-samples the variability of the stratification in the Gulf and we estimate the error associated with single-cast assessments of the stratification.     

Biogeography and phenology of satellite-measured phytoplankton seasonality in the California current

Thirteen years (1998–2010) of satellite-measured chlorophyll a are used to establish spatial patterns in climatological phytoplankton biomass seasonality across the California Current System (CCS) and its interannual variability. Multivariate clustering based on the shape of the local climatological seasonal cycle divides the study area into four groups: two with spring-summer maxima representing the northern and southern coastal upwelling zones, one with a summer minimum offshore in mid-latitudes and a fourth with very weak seasonality in between. Multivariate clustering on the seasonal cycles from all 13 years produces the same four seasonal cycle types and provides a view of the interannual variability in seasonal biogeography. Over the study period these seasonal cycles generally appear in similar locations as the climatological clusters. However, considerable interannual variability in the geography of the seasonal cycles is evident across the CCS, the most spatially extensive of which are associated with the 1997–1999 El Niño-Southern Oscillation (ENSO) signal and the 2005 delayed spring transition off the Oregon and northern and central California coasts. We quantify linear trends over the study period in the seasonal timing of the two seasonal cycles that represent the biologically productive coastal upwelling zones using four different metrics of phenology. In the northern upwelling region, the date of the spring maximum is delaying (1.34 days yr⁻¹) and the central tendency of the summer elevated chlorophyll period is advancing (0.63 days yr⁻¹). In the southern coastal upwelling region, both the initiation and cessation of the spring maximum are delaying (1.78 days yr⁻¹ and 2.44 days yr⁻¹, respectively) and the peak is increasing in duration over the study period. Connections between observed interannual shifts in phytoplankton seasonality and physical forcing, expressed as either basin-scale climate signals or local forcing, show phytoplankton seasonality in the CCS to be influenced by changes in the seasonality of the wind mixing power offshore, coastal upwelling in the near-shore regions and basin-scale signals such as ENSO across the study area.     

Modelling phytoplankton deposition to Chesapeake Bay sediments during winter–spring: interannual variability in relation to river flow

The often-rapid deposition of phytoplankton to sediments at the end of the spring phytoplankton bloom is an important component of benthic–pelagic coupling in temperate and high latitude estuaries and other aquatic systems. However, quantifying the flux is difficult, particularly in spatially heterogeneous environments. Surficial sediment chlorophyll-a, which can be measured quickly at many locations, has been used effectively by previous studies as an indicator of phytoplankton deposition to estuarine sediments. In this study, surficial sediment chlorophyll-a was quantified in late spring at 20–50 locations throughout Chesapeake Bay for 8 years (1993–2000). A model was developed to estimate chlorophyll-a deposition to sediments using these measurements, while accounting for chlorophyll-a degradation during the time between deposition and sampling. Carbon flux was derived from these estimates via C:chl-a = 75.Bay-wide, the accumulation of chlorophyll-a on sediments by late spring averaged 171 mg m⁻², from which the chlorophyll-a and carbon sinking fluxes, respectively, were estimated to be 353 mg m⁻² and 26.5 gC m⁻². These deposition estimates were ∼50% of estimates based on a sediment trap study in the mid-Bay. During 1993–2000, the highest average chlorophyll-a flux was in the mid-Bay (248 mg m⁻²), while the lowest was in the lower Bay (191 mg m⁻²). Winter–spring average river flow was positively correlated with phytoplankton biomass in the lower Bay water column, while phytoplankton biomass in that same region of the Bay was correlated with increased chlorophyll-a deposition to sediments. Responses in other regions of the Bay were less clear and suggested that the concept that nutrient enrichment in high flow years leads to greater phytoplankton deposition to sediments may be an oversimplification. A comparison of the carbon flux associated with the deposition of the spring bloom with annual benthic carbon budgets indicated that the spring bloom did not contribute a disproportionately large fraction of annual carbon inputs to Chesapeake Bay sediments. Regional patterns in chlorophyll-a deposition did not correspond with the strong regional patterns that have been found for plankton net community metabolism during spring.     

Intra-annual variability of extremely rapid sedimentation onto Gardar Drift in the northern North Atlantic

North Atlantic sediment drifts are valuable archives for paleoceanographic reconstructions spanning various timescales. However, the short-term dynamics of such systems are poorly known, and this impinges on our ability to quantitatively reconstruct past change. Here we describe a high-resolution 319-day time-series of hydrodynamics and near-bottom (4 m) particulate matter flux variability at a 2600 m deep site with an extremely high sediment accumulation rate on the southern Gardar Drift in the North Atlantic. We compare our findings with the actual deposits at the site. The total annual particle flux amounted to ～360 g m^?2 yr^?1, varied from ～0.15 to >5.0 g m^?2 day^?1 and displayed strong seasonal compositional changes, with the highest proportion of fresh biogenic matter arriving after the spring bloom in June and July. Flux variability also depended on the changing input of lithogenic matter that had been (re)suspended for a longer time (decades). Active focussing of material from both sources is required to account for the composition and the magnitude of the total flux, which exceed observations elsewhere by an order of magnitude. The enhanced focussing or increased delivery appeared to be positively related to current velocity. The intercepted annual particle flux accounted for only 60% of the sediment accumulation rate of 600±20 g m^?2 yr^?1 (0.20±0.07 cm yr^?1), indicating higher intra- and inter-annual variability of both the biogenic and lithogenic fluxes and/or advection of additional sediment closer to the seafloor (i.e. <4 m). This temporal variability in the composition and amount of material deposited highlights intra-annual changes in the flux of lithogenic material, but also underscores the importance of (reworked) sediment focussing and seasonality of the biogenic flux. All should be taken into account in the interpretation of the paleorecord from such depositional settings.     

Spectral distribution of wave energy dissipation by salt marsh vegetation

Spectral energy dissipation of random waves due to salt marsh vegetation (Spartina alterniflora) was analyzed using field data collected during a tropical storm. Wave data (significant wave heights up to 0.4 m in 0.8 m depth) were measured over a two-day period along a 28 m transect using 3 pressure transducers. The storm produced largely bimodal spectra on the wetland, consisting of low-frequency swell (7–10 s) and high-frequency (2–4.5 s) wind-sea. The energy dissipation varied across the frequency scales with the largest magnitude observed near the spectral peaks, above which the dissipation gradually decreased. The wind-sea energy dissipated largely in the leading section of the instrument array in the wetland, but the low-frequency swell propagated to the subsequent section with limited energy loss. Across a spectrum, dissipation did not linearly follow incident energy, and the degree of non-linearity varied with the dominant wave frequency. A rigid-type vegetation model was used to estimate the frequency-dependent bulk drag coefficient. For a given spectrum, this drag coefficient increased gradually up to the peak frequency and remained generally at a stable value at the higher frequencies. This spectral variation was parameterized by employing a frequency-dependent velocity attenuation parameter inside the canopy. This parameter had much less variability among incident wave conditions, compared to the variability of the bulk drag coefficient, allowing its standardization into a single, frequency-dependent curve for velocity attenuation inside a canopy. It is demonstrated that the spectral drag coefficient predicts the frequency-dependent energy dissipation with more accuracy than the integral coefficient.     

Seasonality of particle-associated trace element fluxes in the deep northeast Atlantic Ocean

In the framework of the German contribution to the Joint Global Ocean Flux Study (JGOFS), deep-water fluxes of particle-associated trace elements were measured in the northeast Atlantic Ocean. The sinking particles were collected almost continuously from 1992 to 1996 at three time-series stations, L1 (33°N/22°W), L2 (47°N/20°W), and L3 (54°N/21°W), using sediment traps. The focus of the present study is the temporal variability of the particle-associated elemental fluxes of Al, Ca, Cd, Co, Cu, Fe, Mn, Ni, P, Pb, Ti, V, and Zn at a depth of 2000 m.A clear seasonality of the fluxes that persisted for several years was documented for the southernmost station (L1) at stable oligotrophic conditions in the area of the North Atlantic Subtropical Gyre East (NASTE). At L2 and L3, an episodic nature of the elemental fluxes was determined. Mesoscale eddies are known to frequently cause temporal and spatial variability in the flux of biogenic components in that area. These events modified the simple seasonal pattern controlled by the annual cycle at L2, in the North Atlantic Drift Region (NADR), and at L3, which was influenced by the Atlantic Arctic province (ARCT). All stations were characterized by an additional episodic lithogenic atmospheric supply reaching the deep sea.The integrated annual fluxes during the multi-year study revealed similar flux magnitudes for lithogenic elements (Al, Co, Fe, Ti, and V) at L2 and L3 and roughly twofold fluxes at L1. Biogenic elements (Cd, P, and Zn) showed the opposite trend, i.e., two to fourfold higher values at L2 and L3 than at L1. For Mn, Ni, and Cu, the spatial differences were smaller, perhaps because of the intermediate behavior, between lithogenic and biogenic, of these elements. Similarly, among the three study sites, there were no noticeable differences in the total annual flux of Pb.The respective lithogenic fractions of the deep-sea fluxes of Cd, Co, Cu, Mn, Ni, V, and Zn were subtracted based on the amount of Al, with the average composition of the continental crust as reference. This procedure allowed estimation of the labile trace element fraction (TE_exc) of the particles, i.e., TE taken up or scavenged during particle production and sedimentation. The ratios of TE_exc/P clearly demonstrated an enrichment of TE over labile P from biogenic surface material to the deep sea for Zn (factor 4–6), Mn (12–27), Ni (3–5), and Cu (9–25); an intermediate status for Co (0.5–2.2); and depletion for Cd vs. P (0.2–0.4). Surprisingly, the recycling behavior of excess Co was found to be similar to that of P. Hence, Co_exc behaved like a biogenic element; this is in contrast to total Co, which is dominated by the refractory lithogenic fraction.Moreover, it is argued that these excess elemental fluxes caused a loss of the dissolved elements in upper waters, since their transport reaches the deep-sea waters at 2000 m, a depth far below of deep-winter mixing and upwelling. The annual amount of excess TE exported from surface waters was estimated to be 1.3×10⁹ mol Zn y^?1, 4.4×10⁹ mol Mn y^?1, 4.9×10⁸ mol Ni y^?1, 2.2×10⁷ mol Cd y^?1, 7.4×10⁸ mol Cu y^?1, and 2.7×10⁷ mol Co y^?1 for the whole North Atlantic Ocean. Important primary sources that could replenish these losses are the aeolian and fluvial supply processes.     

Connectivity clues from short-term variability in settlement and geochemical tags of mytilid mussels

The use of geochemical tags in calcified structures of fish and invertebrates is an exciting tool for investigating larval population connectivity. Tag evaluation over relatively short intervals (weeks) may detect environmental and ecological variability at a temporal scale highly relevant to larval transport and settlement. We collected newly settled mussels (Mytilus californianus and M. galloprovincialis) weekly during winter/spring of 2002 along the coast of San Diego, CA, USA, at sites on the exposed coast (SIO) and in a protected coastal bay (HI), to investigate temporal patterns of geochemical tags in mussel shells. Analyses of post-settlement shell via LA-ICP-MS revealed statistically significant temporal variability for all elements we examined (Mg, Mn, Cu, Sr, Cd, Ba, Pb and U). Despite this, our ability to distinguish multielemental signatures between sites was largely conserved. Throughout our 13-week study, SIO and HI mussels could be chemically distinguished from one another in 78–87% of all cases. Settlement varied between 2 and 27 settlers gram-byssus^?1 week^?1 at SIO and HI, and both sites were characterized by 2–3 weeks with “high” settlement. Geochemical tags recorded in early larval shell of newly settled mussels differed between “high” and “low” settlement weeks at both sites (MANOVA), driven by Mg and Sr at SIO (p = 0.013) and Sr, Cd, Ba and Pb at HI (p < 0.001). These data imply that shifts in larval sources or transport corridors were responsible for observed settlement variation, rather than increased larval production. In particular, increased settlement at HI was observed concurrent with the appearance of geochemical tags (e.g., elevated Cd), suggesting that those larvae were retained in upwelled water near the mouth of the bay. Such shifts may reflect short-term changes in connectivity among sites due to altered transport corridors, and influence the demography of local populations.     

Lunar cycles and seasonal variations in deposition fluxes of planktic foraminiferal shell carbonate to the deep South Atlantic (central Walvis Ridge)

Several authors have argued that lunar reproductive cycling controls the shell fluxes of planktic foraminifera, one of the major carbonate-producing groups in the global pelagic ocean. A time-series sediment trap at 2700 m depth on the central Walvis Ridge below the South Atlantic central gyre demonstrate for the first time that shell deposition fluxes of Hastigerina pelagica are synchronous with lunar periodicity. Spectral analysis of the 6-month time-series with 8-day resolution showed a strong 30-day cyclicity in the flux maxima of H. pelagica arriving at the ocean floor on average 12.5 days after each full moon. Given a shell settling velocity of about 400 m day⁻¹, which implies about 7 days for settling, this coincides with the pronounced endogenous reproduction rhythm of 5±2 days after full moon as originally observed in laboratory-cultured isolates from off Bermuda in the North Atlantic. By contrast, no endogenous or exogenous lunar periodicity was observed in the deposition flux or size distribution of any of the 27 other shell species from austral winter (August 2000) to austral summer (February 2001). Instead, the deposition fluxes of shell species, the bulk carbonate and the total mass were dominated by a seasonal maximum during austral spring, without any periodicity in the 16–90-day domain of this study. Since H. pelagica exhibits low fluxes with a low burial efficiency, and continuous (re)production is shown by the deposition fluxes of other species, lunar reproductive cycling appears not to affect pelagic carbonate productivity and deep ocean sedimentation fluxes.     

Deep-sea suprabenthos assemblages (Crustacea) off the Balearic Islands (western Mediterranean): Mesoscale variability in diversity and production

The composition of suprabenthic crustacean assemblages, their diversity, production (P) and production/biomass (P/B) ratios, were analyzed at species level along two transects situated to the north (N) and south (S) of Mallorca (Balearic Islands, western Mediterranean) at depths between 134 m and 760 m, based on a ca. bi-monthly sampling performed between August 2003 and June 2004. Differences with depth and season in assemblage composition and diversity were analyzed as a function of the contrasting environmental features (e.g. water mass dynamics) of the two areas. We identified 187 species (18 decapods, 5 euphausiids, 16 mysids, 76 gammaridean amphipods, 13 hyperiids, 1 caprellid, 21 isopods and 37 cumaceans). Substantial mesoscale variability in the deep-sea suprabenthic assemblages coupled with diversity trends between the N and S transects were found. Seasonality was the most important gradient influencing the dynamics of suprabenthos over the upper (350 m) and middle (650–750 m) slope in the N area. Conversely, the S area appeared to be more stable temporally with depth as the main gradient inducing assemblage differences. Different depth-related patterns were observed both for diversity and P/B. To the north diversity was very low at the shelf-break, increasing on the upper-slope (H′ > 3.00) and then decreasing again on the middle-slope. To the south diversity increased smoothly downward, reaching the highest values on the middle-slope. Regarding productivity, P/B was highest at intermediate depths to the north (over ca. 450–500 m), while to the south highest P/Bs were found deeper (over ca. 600–650 m). The higher P/B at intermediate depths found along N are likely due to higher % of organic matter (OM) in sediments, a product of oceanographic frontal systems. In particular, P/B was higher along N among omnivores and detritus feeders (e.g. Andaniexis mimonectes, Lepechinella manco and combined cumaceans), coupled to enriched OM in sediments, while along S mesoplanktonic carnivores (Rhachotropis spp.) had higher P/Bs. We conclude that on the north slope the influence of frontal systems and more active flow dynamics of different water masses (WIW and LIW) increases natural disturbance in the area, increasing productivity and diversity of suprabenthic peracarids in the Benthic Boundary Layer. Also, species showed a displacement of their average distributions (their Centres of Gravity, CoG) to shallower depths along N, which is another indicator of more favorable habitat conditions for suprabenthos in the 400–500 m range at N.     

Wave climate variability in the North-East Atlantic Ocean over the last six decades

Ocean surface gravity waves play a major role in many engineering and environmental problems, both in the open ocean and in coastal zones. Therefore, it is essential to improve our knowledge on spatial and temporal variability of wave climate. This study aims at investigating this variability in the North-East Atlantic Ocean (25°W–0°W and 30°N–60° N), using a 57-year hindcast (1953–2009) obtained with a spectral wave model forced with reanalysis wind fields. The hindcast analysis reveals firstly strong seasonal fluctuations of wave climate, with winters characterized by large and long-period waves of mean direction spreading from south-west to north-west, and summers characterized by smaller and shorter-period waves originating from norther directions. From northern (55°N) to southern (35°N) latitudes, the significant wave height (Hs) decreases by roughly 40%, the mean wave direction (Mwd) rotates clockwise by about 25% while the peak period (Tp) only grows by 5%. These three parameters also exhibit a strong inter-annual variability, particularly when winter-means (from 1st of December to 1st of April) are considered. Linear trend analysis over the studied period shows spatially variable long-term trends, with a significant increase of Hs (up to 0.02 m yr^?1) and a counterclockwise shift of Mwd (up to ?0.1° yr^?1) at northern latitude, contrasting with a fairly constant trend for Hs and a clockwise shift of Mwd (up to +0.15° yr^?1) at southern latitudes. Long-term trends of Tp are less significant, with still a slight increase in the north-eastern part of the study area (up to +0.01 s yr^?1). Eventually, a comparison between the inter-annual variability of the winter-means of the three selected wave parameters and the North Atlantic Oscillation (NAO) reveals: (1) a strong positive correlation between Hs and the NAO index at northern latitudes (correlation coefficient up to R = 0.91) and a significant negative correlation at southern latitudes (up to R = ?0.6); (2) no significant correlation for Mwd north of 40°N and a clear positive correlation southward of 40°N (up to R = 0.8) and (3) a northward increasing correlation for Tp (up to R = 0.8). Long-term trends for Hs, Mwd and Tp are finally explained by a significant increase in the NAO index over the studied period.     

Spatial and temporal variations in sediment accumulation and their impacts on coral communities in the Sanya Coral Reef Reserve,Hainan, China

This study investigated the spatial and temporal variations of sediment accumulation and their impacts on coral communities in four sites at two or three depths (3 m, 6 m and 9 m) at the Sanya Coral Reef Reserve by deploying sediment traps on the sea floor during 2007–2009. Rainfall and typhoon events, which appeared to control sediment accumulation in the sea floor of the coral reef, were positively correlated with total sediment and sand-sized (i.e. 63–2000 µm) sediment accumulation. Sediment accumulation rate significantly decreased with the distance far away from the coast in Sanya. The mean sediment accumulation rates in Ximaozhou, Luhuitou and Xiaodonghai during 2007 to 2009 were close to 20 mg cm⁻² d⁻¹, and they were significantly higher than that in Yalongwan, probably as a result of terrestrial soil erosion caused by strong coast human activities (e.g. coastal construction, dredging and hillside clearing). Correlation analysis revealed that silt-clay-sized sediment accumulation rate was highly negatively correlated with total live coral cover and coral cover in some taxa, such as Montipora and branching Porites. whereas, Diploastrea heliopora was positively correlated with silt-clay-sized sediment accumulation. Correlation analysis also suggested that silt-clay-sized sediment accumulation had a higher efficiency in predicting the spatial variation of total live coral cover in Sanya than did the total sediment accumulation. Based on this investigation, we conclude that high rates of sediment accumulation pose a severe threat to the Sanya Coral Reef Reserve, highlighting the importance of integrated watershed management practices in the Sanya Coral Reef Reserve.     

Distribution of deep-water corals along the North American continental margins: Relationships with environmental factors

Despite the increasing attention to assemblages of deep-water corals in the past decade, much of this research has been focused on documenting and enumerating associated fauna. However, an understanding of the distribution of most species of coral and the ecological processes associated with these assemblages is still lacking. In this study, we qualitatively and quantitatively described the habitats of two families of deep-water corals in relation to six oceanographic factors (depth, slope, temperature, current, chlorophyll a concentration and substrate) on the Pacific and Atlantic Continental Margins of North America (PCM and ACM study areas, respectively). This study focused primarily on the distributions of Primnoidae and Paragorgiidae because of the large number of documented occurrences. For each environmental factor, deep-water coral locations were compared to the surrounding environment using χ² tests. On both continental margins, coral locations were found to be not randomly distributed within the study areas, but were within specific ranges for most environmental factors. In the PCM study area, Paragorgiidae and Primnoidae locations were found in areas with slopes ranging from 0° to 10.0°, temperature from −2.0 to 11.0 °C and currents from 0 to 143 cm s⁻¹. In the ACM study area, Paragorgiidae and Primnoidae locations were found in areas with slopes ranging from 0° to 1.4°, temperature ranging from 0 to 11.0 °C and currents ranging from 0 to 207 cm s⁻¹. Although the patterns in habitat characteristics were similar, differences existed between families with respect to particular environmental factors. In both study areas, most environmental parameters in locations where corals occurred were significantly different from the average values of these parameters as determined with χ² tests ($p<0.05$) except for substrate in Paragorgiidae locations and depth in Primnoidae locations on the PCM. This is the first study to show coral distributional patterns at the continental shelf/slope scale.     

Biogeochemical responses to late-winter storms in the Sargasso Sea,I—Pulses of primary and new production

We have hypothesized that the weekly/biweekly passage of winter storms in the subtropical open ocean destabilizes the water column leading to pulsed NO₃^? inputs, resulting in new production that is not accounted for in most annual estimates. This paper presents data on nitrogen and carbon cycling in the Sargasso Sea at approximately daily resolution, during the period prior to seasonal stratification in 2004 and 2005; these data permit us to assess the importance of winter storms for introducing NO₃^? and the contribution of these inputs to annual new and export production. The two sampling years were in stark contrast to each other with 2004 characterized by periods of relative calm between winter storms, and 2005 characterized by nearly continuous storm activity. As a result, temporal variability in mixed layer depth (MLD) and euphotic zone [NO₃^?] were very different between years. MLDs in 2004 increased to >150 m in response to the passage of storms and then rapidly shoaled to <100 m leading to the pulsed injection of NO₃^? (～100 nmol l^?1) into the lower half of the euphotic zone, while in 2005 MLDs were consistently >300 m and euphotic zone [NO₃^?]>100 nmol l^?1. Despite the very different [NO₃^?], rates of daily NO₃^? uptake were similar from year to year because of significant nocturnal uptake in 2004. Similar rates of new production did not translate into similar rates of particulate nitrogen and carbon export however, as observed export from the upper 200 m was 2–5-fold greater in 2004 than in 2005. Furthermore, the decrease of particulate nitrogen and carbon flux with depth between 200 and 400 m in 2004 was substantially lower than in 2005; this is consistent with the observed biological response in which diatoms and coccolithophores exhibited rapid growth following pulsed NO₃^? inputs in 2004. A combination of data from the Bermuda Testbed Mooring, which provides a longer temporal record than the cruise, and the observations presented in this study show that in the winter of 2004, there were 8–10 storm events that likely resulted in pulsed NO₃^? inputs. Summed over all the events, new production prior to seasonal stratification was estimated to be ～0.12–0.18 mol N m^?2 or ～14–21% of current annual estimates.     

High-frequency fluxes of labile compounds in the central Ligurian Sea,northwestern Mediterranean

Sinking particles were collected every 4 h with drifting sediment traps deployed at 200 m depth in May 1995 in a 1-D vertical system during the DYNAPROC observations in the northwestern Mediterranean sea. POC, proteins, glucosamine and lipid classes were used as indicators of the intensity and quality of the particle flux. The roles of day/night cycle and wind on the particle flux were examined. The transient regime of production from late spring bloom to pre-oligotrophy determined the flux intensity and quality. POC fluxes decreased from, on average, 34 to 11 mg m⁻² d⁻¹, representing 6–14% of the primary production under late spring bloom conditions to 1–2% under pre-oligotrophic conditions. Total protein and chloroplast lipid fluxes correlated with POC and reflected the input of algal biomass into the traps. As the season proceeded, changes in the biochemical composition of the exported material were observed. The C/N ratio rose from 7.8 to 12. Increases of serine (10–28% of total proteins), total lipids (7–9 to 14–28% of POC) and reserve lipids (1–5 to 5–22% of total lipids) were noticeable, whereas total protein content in POC decreased (20–27 to 18–7%). N-acetyl glucosamine, a tracer of fecal pellet flux, showed that zooplankton grazing was a major vector of downward export during the decaying bloom. Against this background pattern, episodic events specifically increased the flux, modifying the quality and the settling velocity of particles. Day/night signals in biotracers (POC, N-acetyl glucosamine, protein and chloroplast lipids) showed that zooplankton migrations were responsible for sedimentation of fresh material through fast sinking particles (V=170–180 m d⁻¹) at night. Periodic signatures of re-processed material (high lipolysis and bacterial biomass indices) suggested that other zooplankton fecal pellets or small aggregates, probably of lower settling velocities (V<170 m d⁻¹), contributed to the flux during calm periods. At the beginning of the experiment, during the development of a prymnesiophyte bloom in the upper layers, the sterol signal with no periodicity enabled us to estimate high particle settling velocities (⩾600 m d⁻¹) likely related to large aggregate formation. A wind event increased biotracer fluxes (POC, protein, chloroplast lipids). The rapid transmission of surface signals through extremely fast sinking particles could be a general feature of particle fluxes in marine areas unaffected by horizontal advection.     

Dissolved inorganic carbon,alkalinity, nutrient and oxygen seasonal and interannual variations at the Antarctic Ocean JGOFS-KERFIX site

JGOFS-KERFIX (KERguelen point FIXe) time-series station, located south of the polar front in the Indian sector of the Antarctic Ocean, was occupied monthly between January 1990 and March 1995. Annual cycles of dissolved inorganic carbon (DIC), total alkalinity (TALK), oxygen (O₂) and nutrients (nitrate, silicate, phosphate and ammonia) in the upper ocean are presented for this site. From seasonal drawdown of nutrients and DIC, we estimate a spring–summer net community production of 3.2±0.5 mol m⁻² and C/N/P ratios of 100/16/1. The Si/N ratio varies between 1.8 and 3, suggesting low iron concentrations. The spring–summer biogenic silicon export derived from silicate drawdown is 1.18 mol m⁻², consistent with model estimates of silicate export at this site. Seasonal and interannual variations of oxygen, nitrate and DIC due to physical and biological processes are quantified using a simple month-to-month budget formulation. From these budgets, an annual net community production of 5.7±3.3 mol m⁻² yr⁻¹ is estimated, about twice the averaged spring–summer production, indicating that, at KERFIX, there is a positive net community production throughout the year. Air–sea CO₂ fluxes show that KERFIX is a strong CO₂ sink for the atmosphere of 2.4–5.1 mol m⁻² yr⁻¹ in 1993, depending on the gas exchange formulation used. A 2.1–3.3 mol m⁻² yr⁻¹ outgassing of O₂ is observed at KERFIX except in 1993 and 1994 where a decreasing trend of temperature induces an increase of O₂ solubility.     

Tropical Atlantic coral oxygen isotopes: glacial–interglacial sea surface temperatures and climate change

We have generated a detailed oxygen isotope time-series from the fossil coral reefs from offshore Barbados. The Barbados coral-based record is a unique paleoceanographic data set with an equivalent sedimentation rate in excess of 600 cm/kyr where not only is the annual signal uniquely preserved but seasonality as well. Oxygen isotope values during the late glacial and LGM (16–20 ¹⁴C kyrs; 19–24 calendar kyrs) are ∼2.3‰ heavier than corresponding living specimens, and indicate a regional cooling on the order of 4.5°C. There is also an isotopic expression of the Bølling-Pre-Boreal climate oscillation, with values reflecting a cooling during the Younger Dryas. Seasonality, a key diagnostic of the state of the climate system, remained the same or slightly less than present and indicates that the observed coolings were a change in the mean state of the western tropical Atlantic. Pan-tropic cooling during the last glaciation is best explained by a change in the radiative balance of the tropics. Variable tropical sea surface temperatures during climate oscillations such as the Younger Dryas challenge the paradigm that climate change only cascades from variations in North Atlantic deep water production.     

Microbialite development patterns in the last deglacial reefs from Tahiti (French Polynesia; IODP Expedition #310): Implications on reef framework architecture

The widespread occurrence of microbialites in the last deglacial reef frameworks (16–6 Ka BP) implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea-level variations and environmental changes.The present study is based on the sedimentological and chronological analysis (¹⁴C AMS dating) of drill cores obtained during the IODP Expedition #310 “Tahiti Sea Level” on the successive terraces which typify the modern reef slopes from Tahiti. It provides a comprehensive data base to investigate the microbialite growth patterns (i.e. growth rates and habitats), to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea-level rise.The last deglacial reefs from Tahiti are composed of two distinctive biological communities: (1) the coralgal communities including seven assemblages characterized by various growth forms (branching, robust branching, massive, tabular and encrusting) that form the initial frameworks and (2) the microbial communities developed in the primary cavities of those frameworks, a few meters (1.5 to 6 m) below the living coral reef surface, where they heavily encrusted the coralgal assemblages to form microbialite crusts. The dating results demonstrate the occurrence of two distinctive generations of microbialites: the “reefal microbialites” which developed a few hundred years after coralgal communities in shallow-water environments, whereas the “slope microbialites” grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities.The development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies. The most widespread microbialite development occurred in frameworks dominated by branching, thin encrusting, tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity (> 50%). In contrast, their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity (~ 30%) and could not host a significant microbialite expansion.