Intense Upwelling Research Articles

On the factors influencing the development of sporadic upwelling in the Leeuwin Current system

[1] While there is no persistent upwelling along the West-Australian (WA) coastline, sporadic upwelling events have been documented primarily in summer. By analyzing comparatively the variability of both Ekman and geostrophic cross-shore transports over a seasonal cycle, we show that the situation is more contrasted. Based on a composite index computed from satellite data over a 15 year period, calibrated with well documented events, we investigate the factors influencing the development of sporadic upwelling in the region. Overall, the occurrence of transient upwelling events lasting 3–10 days varies largely in space and time. Shelf regions at 31.5 and 34°S are favored with up to 12 upwelling days per month during the austral spring/summer. Although being generally favored from September to April, sporadic upwelling events can also occur at any time of the year at certain locations north of 30°S. On average over 1995–2010, the Ningaloo region (22.5°S) cumulates the highest number of upwelling (∼140 days per year) and is characterized by longer events. The intensity of intermittent upwelling is influenced by the upwelling-favorable winds, the characteristics of the Leeuwin Current (e.g., onshore geostrophic flow, mesoscale eddies and meanders, stratification and nitracline) and the local topography. This suggests that short-living nutrient enrichment of variable magnitude may occur at any time of the year at many locations along the WA coast.

Combined analyses of kinship and FST suggest potential drivers of chaotic genetic patchiness in high gene-flow populations.

We combine kinship estimates with traditional F-statistics to explain contemporary drivers of population genetic differentiation despite high gene flow. We investigate range-wide population genetic structure of the California spiny (or red rock) lobster (Panulirus interruptus) and find slight, but significant global population differentiation in mtDNA (ΦST = 0.006, P = 0.001; Dest_Chao = 0.025) and seven nuclear microsatellites (FST = 0.004, P < 0.001; Dest_Chao = 0.03), despite the species’ 240- to 330-day pelagic larval duration. Significant population structure does not correlate with distance between sampling locations, and pairwise FST between adjacent sites often exceeds that among geographically distant locations. This result would typically be interpreted as unexplainable, chaotic genetic patchiness. However, kinship levels differ significantly among sites (pseudo-F16,988 = 1.39, P = 0.001), and ten of 17 sample sites have significantly greater numbers of kin than expected by chance (P < 0.05). Moreover, a higher proportion of kin within sites strongly correlates with greater genetic differentiation among sites (Dest_Chao, R2 = 0.66, P < 0.005). Sites with elevated mean kinship were geographically proximate to regions of high upwelling intensity (R2 = 0.41, P = 0.0009). These results indicate that P. interruptus does not maintain a single homogenous population, despite extreme dispersal potential. Instead, these lobsters appear to either have substantial localized recruitment or maintain planktonic larval cohesiveness whereby siblings more likely settle together than disperse across sites. More broadly, our results contribute to a growing number of studies showing that low FST and high family structure across populations can coexist, illuminating the foundations of cryptic genetic patterns and the nature of marine dispersal.

Upwelling‐influence, macroalgal blooms, and seagrass production; temporal trends from latitudinal and local scales in northeast Pacific estuaries

In coastal marine systems worldwide, land‐based nutrient inputs are often correlated with blooms of macroalgae, which can negatively affect seagrass habitats. We used spatiotemporal trends in production to identify the role of marine‐derived nutrients in mediating these interactions. Among ocean upwelling‐influenced estuaries along the northeastern Pacific, we documented a negative correlation between annual production of ulvoid macroalgae and the seagrass, Zostera marina L., at a regional scale that included four estuaries along a ∼ 400 km distance. While macroalgal biomass was ∼ 30 times greater in southern (Yaquina Bay and Coos Bay, Oregon) compared to northern (Willapa Bay, Washington, and Netarts Bay, Oregon) estuaries, no temporal patterns of eelgrass decline were observed within the estuaries over a 5 yr period. Latitudinally, 65% of the between‐site ordination variance in interannual macrophyte production was associated with ocean upwelling; macroalgae was positively correlated, and eelgrass negatively correlated with more intense upwelling. Within one estuary, Coos Bay, we found that land‐based nutrients had no effect on macrophyte productivity. Instead, a little more than a third of the variation was explained by upwelling (marine dissolved inorganic nitrogen and salinity) and climate (photosynthetically active radiation). Thus, contrary to the paradigm of negative effects of macroalgae on eelgrass, we found correlative evidence that ocean upwelling and local estuarine conditions could be responsible for these large biogeographic patterns.

The eastern Mediterranean phosphorite giants: An interplay between tectonics and upwelling

ABSTRACT About 20 billion tonnes of world-class, high-grade phosphorite resources occur in a small area of the eastern Mediterranean region, including Jordan, northern Negev (Palestine), northwestern Saudi Arabia, western Iraq, and southeastern Syria. Major deposits were formed during Campanian to Eocene times and contribute significantly to the economic development of these countries, particularly Jordan and Syria. The phosphorite deposits consist mainly of reworked granular material. The phosphate particles are peloids, such as pellets, intraclasts, nodules, coated grains and coprolites, and vertebrate fragments (bone and teeth). The phosphorite sequences are associated with extensive bedded chert, porcelanite, and organic-rich marls. The main phosphate mineral is francolite, a carbonate-rich variety of fluorapatite that has a relatively enhanced uranium content as a result of substitution for calcium in its crystal structure. Two factors are deemed responsible for the deposition of the phosphorites and their associated chert, porcelanite, and marl within this relatively restricted area. The first was a compressional event associated with the initial collision of the oceanic forefront of the Afro-Arabian Plate with the subduction trench of Eurasia that began in Turonian times and continued into the Eocene. This event resulted in gentle folding that produced the Syrian Arc, the Ha’il, Rutba, and Sirhan paleohighs and the Ga’ara Dome, which were loci for the deposition of phosphorites. The second factor was the obstruction and consequent upwelling of oceanic currents by these tectonic highs, enhanced by winds blowing from east to west along the southern platform margin of the Neo-Tethys Ocean. The intense upwelling was associated with the Tethyan Circumglobal Current that flowed along the Afro-Arabian platform on the southern margin of the Neo-Tethys Ocean. In contrast, relatively minor phosphorite deposition took place to the north in southern Europe. The upwelling spread cold, nutrient-rich oceanic water from the deep Neo-Tethys Ocean to the surface, thereby enhancing bioproductivity to produce organic-rich sediments. The subsequent authigenesis of phosphorites, their diagenesis and the reworking and winnowing of the phosphorite-rich sediments, concentrated the materials into economic deposits. Phosphorite deposition ended in the Late Eocene following the final collision of the Afro-Arabian Plate with Eurasia. The sub-aerial exposure of this formerly productive shallow-marine platform was the result of the separation of the Arabian Plate from the African Plate during the mid-Miocene.

Foraminiferal faunal evidence for Glacial–Interglacial variations in the ocean circulation and the upwelling of the Gulf of Tehuantepec (Mexico)

Abstract Three marine sediment cores from the Gulf of Tehuantepec (Eastern Tropical North Pacific) were used to determine variations in upwelling intensity and surface circulation patterns over the last 26 kyr BP. Changes in foraminiferal assemblages at glacial-interglacial timescale indicate a sequence of three major palaeoceanographic events in the study area: (1) The Late Pleistocene (including the Last Glacial Maximum, LGM), dominated by a Neogloboquadrina dutertrei–Globorotalia menardii assemblage, indicative of a stable thermocline, stratified water column and greater persistence of warm equatorial waters in the region. (2) The Termination 1, dominated by a Globigerinita glutinata assemblage, which indicates mixed surface water and transitional conditions between upwelling and stratified water column episodes. Changes in sedimentation rates and a clear reduction of the faunal abundances at this time, could be the result of eustatic sea level change. (3) The Holocene, dominated by a Globigerina bulloides–Globigerinoides ruber assemblage, indicates periods of elevated productivity, intense upwelling and the establishment of the modern ocean conditions. These findings are consistent with climate model results that suggest that regional surface ocean and upwelling conditions are mostly linked to changes in atmospheric circulation over the Laurentide Ice Sheet and shifts in the latitudinal position of the Intertropical Convergence Zone.

Low- to high-productivity pattern within Heinrich Stadial 1: Inferences from dinoflagellate cyst records off Senegal

In order to investigate a possible connection between tropical northeast (NE) Atlantic primary productivity, Atlantic meridional overturning circulation (AMOC), and drought in the Sahel region during Heinrich Stadial 1 (HS1), we used dinoflagellate cyst (dinocyst) assemblages, Mg/Ca based reconstructed temperatures, stable carbon isotopes (δ13C) and geochemical parameters of a marine sediment core (GeoB 9508-5) from the continental slope offshore Senegal. Our results show a two-phase productivity pattern within HS1 that progressed from an interval of low marine productivity between ~19 and 16kyr BP to a phase with an abrupt and large productivity increase from ~16 to 15kyr BP. The second phase is characterized by distinct heavy planktonic δ13C values and high concentrations of heterotrophic dinocysts in addition to a significant cooling signal based on the reconstructions of past sea surface temperatures (SSTs). We conclude that productivity variations within HS1 can be attributed to a substantial shift of West African atmospheric processes. Taken together our results indicate a significant intensification of the North East (NE) trade winds over West Africa leading to more intense upwelling during the last millennium of HS1 between ~16 and 15kyr BP, thus leaving a strong imprint on the dinocyst assemblages and sea surface conditions. Therefore, the two-phase productivity pattern indicates a complex hydrographic setting suggesting that HS1 cannot be regarded as uniform as previously thought.

Finescale Vertical Structure of the Upwelling System off Southern Peru as Observed from Glider Data

Abstract The upwelling system off southern Peru has been observed using an autonomous underwater vehicle (a Slocum glider) during October–November 2008. Nine cross-front sections have been carried out across an intense upwelling cell near 14°S. During almost two months, profiles of temperature, salinity, and fluorescence were collected at less than 1-km resolution, between the surface and 200-m depth. Estimates of alongshore absolute geostrophic velocities were inferred from the density field and the glider drift between two surfacings. In the frontal region, salinity and biogeochemical fields displayed cross-shore submesoscale filamentary structures throughout the mission. Those features presented a width of 10–20 km, a vertical extent of ~150 m, and appeared to propagate toward the shore. They were steeper than isopycnals and kept an aspect ratio close to f/N, the inverse of the Prandtl ratio. These filamentary structures may be interpreted mainly as a manifestation of submesoscale turbulence through stirring of the salinity gradients by the mesoscale eddy field. However, meandering of the front or cross-frontal wind-driven instabilities could also play a role in inducing vertical velocities.

Somatic and molt production in Euphausia mucronata off central-southern Chile: the influence of coastal upwelling variability

Seasonal and inter-annual variability in population abundance, biomass, and somatic and molt production of the Humboldt Current krill Euphausia mucronata were studied during a monthly time series (August 2002 to June 2007) at Stn 18 (36° 30' S, 73° 07' W) off central-southern Chile. Experimental measurements in krill were performed at Stn 18 (in 2007 and 2008) and north- ern Chile (2010) in order to estimate vital rates for use in E. mucronata secondary production calculation at Stn 18. Coastal upwelling intensity was the main oceanographic process found to control E. mucronata population abundance and biomass production on seasonal and inter-annual time scales. Spawning peaks and population structure indicate that E. mucronata produces at least 2 generations per year. The main spawning period occurs during the austral spring when phytoplankton concentration is high. A second, less intense spawning period occurs at the end of the austral summer and early autumn. E. mucronata had a mean biomass of 100 mg C m �3 and an integrated annual secondary production of 2432 mg C m �3 yr �1 , with an overall production/ biomass ratio (P/B) ratio of 24. In May 2007, a maximum daily integrated biomass of 5 g C m �3 and total daily secondary production of 63 mg C m �3 d �1 were observed. These estimates are consider- ably higher than those reported for other krill species in coastal upwelling regions. Multivariate analyses indicate that upwelling-favorable winds promote high E. mucronata biomass and sec- ondary production, but higher abundance and biomass were found during the transition periods from upwelling to downwelling conditions. Results suggest that E. mucronata has a highly effi- cient behavioral strategy to attain high production rates and recover rapidly from potential off- shore losses due to advective processes in a highly productive coastal upwelling ecosystem.

Spatio-temporal variation of microphytoplankton in the upwelling system of the south-eastern Arabian Sea during the summer monsoon of 2009

The phytoplankton standing crop was assessed in detail along the South Eastern Arabian Sea (SEAS) during the different phases of coastal upwelling in 2009. During phase 1 intense upwelling was observed along the southern transects (8°N and 8.5°N). The maximum chlorophyll a concentration (22.7mgm −3) was observed in the coastal waters off Thiruvananthapuram (8.5°N). Further north there was no signature of upwelling, with extensive Trichodesmium erythraeum blooms. Diatoms dominated in these upwelling regions with the centric diatom Chaetoceros curvisetus being the dominant species along the 8°N transect. Along the 8.5°N transect pennate diatoms like Nitzschia seriata and Pseudo-nitzschia sp. dominated. During phase 2, upwelling of varying intensity was observed throughout the study area with maximum chlorophyll a concentrations along the 9°N transect (25mgm−3) with Chaetoceros curvisetus as the dominant phytoplankton. Along the 8.5°N transect pennate diatoms during phase 1 were replaced by centric diatoms like Chaetoceros sp. The presence of solitary pennate diatoms Amphora sp. and Navicula sp. were significant in the waters off Kochi. Upwelling was waning during phase 3 and was confined to the coastal waters of the southern transects with the highest chlorophyll a concentration of 11.2mgm−3. Along with diatoms, dinoflagellate cell densities increased in phases 2 and 3. In the northern transects (9°N and 10°N) the proportion of dinoflagellates was comparatively higher and was represented mainly by Protoperidinium spp., Ceratium spp. and Dinophysis spp.

Interannual variability in sea surface temperature and fCO2 changes in the Cariaco Basin

We examined the variability of sea surface carbon dioxide fugacity (fCO2sea) and its relation to temperature at the Cariaco Basin ocean time-series location (10°30′N, 64°40′W) for the period from 1996 through 2008. Periods of warm (positive) and cold (negative) anomalies at the station were related to variability in coastal upwelling intensity. A positive temporal trend in monthly-deseasonalized sea surface temperatures (SST) was observed, leading to an overall increase of 1.13°C over 13 years. Surface fCO2sea displayed significant short-term variation (month to month) with a range of 330–445μatm. In addition to a large seasonal range (58±17μatm), deseasonalized fCO2sea data showed an interannual positive trend of 1.77±0.43μatmyr−1. In the Cariaco Basin, positive and negative anomalies of temperature and fCO2sea are in phase. An increase/decrease of 1°C coincides with an increase/decrease of 16–20μatm of fCO2sea. Deseasonalized fCO2sea normalized to 26.05°C, the mean Cariaco SST, shows a lower rate of increase (0.51±0.49μatmyr−1). Based on these observations, 72% of the increase in fCO2sea in Cariaco Basin between 1996 and 2008 can be attributed to an increasing temperature trend of surface waters, making this the primary factor controlling fugacity at this location. During this period, a decrease in upwelling intensity was also observed. The phytoplankton community changed from large diatom-dominated blooms during upwelling in the late 1990's to blooms dominated by smaller cells in the first decade of the 21st century. The average net sea-air CO2 flux over the study period is 2.0±2.6molCm−2yr−1 employing the Wanninkhof parameterization, and 2.1±2.5molCm−2yr−1 based on Nightingale's model. To further understand the connection between the changes observed in the Cariaco Basin, the relationships between interannual variability in the temperature anomaly with three modes of climate variability (AMO, NAO and ENSO) were examined. The correlations between SSTA and two of these climate modes (AMO and ENSO) only show very weak relationships, although they were significant.

Impact of Inter-annual Coastal Upwelling Variability (2001-2010) on the Productivity of the Moroccan Atlantic South Area (21° - 26°N)

Impact of Inter-annual Coastal Upwelling Variability (2001-2010) on the Productivity of the Moroccan Atlantic South Area (21° - 26°N) The pelagic ecosystem of the Moroccan Atlantic coast is mainly governed by the upwelling variability. The area between Cape Boujdor (26°N) and Cape Blanc (21°N) was water sampled annually during winter and summer from 2000 to 2010. This area is characterized by intense coastal upwelling which’s highly variable (seasons and in space basis) and with an active centre localized at 25° 30’N section. Additionally to the in-situ data, satellite data was used for a synoptic view and for a complementary inter- annual study of upwelling impact on the coastal ecosystem. Evolution of physical and chemical parameters such as temperature (in situ and from satellite), salinity and nutrients, display a low activity of upwelling during the last autumn (2010) in comparison with the high activity during 2007- 2008.

Marine Radiocarbon Reservoir Effect in Southern Atlantic Iberian Coast

Research concerning the variability of the marine radiocarbon reservoir effect (ΔR) in the southern Iberian Atlantic coast confirms the existence of different ΔR values for regions that correspond to different oceanographic conditions. Due to these oceanographic conditions, the southern Iberian Atlantic coast can be divided into 3 zones: the Barlavento (windward), where the coastal waters are influenced by an intense upwelling of the northeastern Atlantic circulation (positive ΔR values); the Sotavento (leeward), where an upwelling area of minor intensity occurs; and the Andalusian coast, where because of its configuration does not present any wind-driven coastal upwelling (negative ΔR values). For the first time, ΔR values were determined for the Sotavento coastal region and, at the same time, new ΔR values were calculated for the Barlavento and the Andalusian coast for the last 3000 yr taking into account the data already obtained but now using a new methodology for calculation. In this way, ΔR weighted mean values were determined for the 3 regions of the southern Iberian Atlantic coast: ΔR = +69 ± 17 14C yr (Barlavento), ΔR = −26 ± 14 14C yr (Sotavento), and ΔR = −108 ± 31 14C yr (Andalusian coast). These values are in accordance with the different oceanographic conditions prevailing in these coastal regions. The data also allow identification of a Bond event at 0.8 ka cal BP and a drastic change in the oceanographic conditions in the Barlavento and Andalusian coastal areas during the 5th millennium cal BP.

Development Under ElevatedpCO2Conditions Does Not Affect Lipid Utilization and Protein Content in Early Life-History Stages of the Purple Sea Urchin,Strongylocentrotus purpuratus

Ocean acidification (OA) is expected to have a major impact on marine species, particularly during early life-history stages. These effects appear to be species-specific and may include reduced survival, altered morphology, and depressed metabolism. However, less information is available regarding the bioenergetics of development under elevated CO(2) conditions. We examined the biochemical and morphological responses of Strongylocentrotus purpuratus during early development under ecologically relevant levels of pCO(2) (365, 1030, and 1450 μatm) that may occur during intense upwelling events. The principal findings of this study were (1) lipid utilization rates and protein content in S. purpuratus did not vary with pCO(2); (2) larval growth was reduced at elevated pCO(2) despite similar rates of energy utilization; and (3) relationships between egg phospholipid content and larval length were found under control but not high pCO(2) conditions. These results suggest that this species may either prioritize endogenous energy toward development and physiological function at the expense of growth, or that reduced larval length may be strictly due to higher costs of growth under OA conditions. This study highlights the need to further expand our knowledge of the physiological mechanisms involved in OA response in order to better understand how present populations may respond to global environmental change.

Estimates of potential new production in the Java-Sumatra upwelling system

The Java-Sumatra upwelling is one of the most important upwelling systems in the Indian Ocean, with maximum upwelling intensity in July through August. To estimate the nitrate supplied by upwelling, we developed a three-dimensional hydrodynamic model to calculate the mean vertical speed and determine the depth of upwelling. We used in-situ vertical nitrate profiles to assess nitrate concentration in the upwelled waters, and calculated the nitrate supply as the product of nitrate concentration and vertical transport obtained from the numerical model. The calculated result represents potential new production generated in the upwelling region. We found that on the event time scale (monthly) of Java-Sumatra upwelling, water brought to the surface originated from locations 100-m deep, giving a nitrate supply of 93.77×103 mol/s and potential new production of 1.02×1014 gC/a.

Downhole variation of lithium and oxygen isotopic compositions of oceanic crust at East Pacific Rise, ODP Site 1256

Bulk rock lithium and oxygen isotope compositions from ODP Site 1256 were analyzed to investigate the seawater circulation in the upper oceanic crust formed at the East Pacific Rise (EPR). The upper extrusive basalts have δ18O values from +6.1‰ to +9.2‰, reflecting alteration of oceanic crust by seawater at low temperatures (&lt;200–250°C). Bulk rocks from the sheeted dike complex and plutonic section have overall lower δ18O values (+3.0‰–+5.5‰). In the sheeted dike complex bulk rock δ18O values gradually decrease with depth, and then increase toward the fresh MORB δ18O value after reaching a minimum of +3.0‰ at ∼1350 m below seafloor (mbsf). The entire sampled crust is dominated by rocks with low lithium contents relative to fresh MORBs except for a few localized Li enrichment. The upper volcanic zone is characterized by a spread of δ7Li from low to high values relative to average unaltered MORB values (δ7Li = +3.4 ± 1.4‰). The presence of rocks with low δ7Li values in the upper crust most likely indicates zones of upwelling of relatively hot (∼200–250°C) hydrothermal fluids. In the sheeted dike complex, bulk rock δ7Li values show wide range of variation, but exhibit a general trend from enriched to depleted values at ∼1280 mbsf and then return to that for fresh MORB within the upper tens of meters of the plutonic section at the bottom of the after reaching a minimum at ∼1350 mbsf (δ7Li = −1.6‰). The downhole pattern of δ7Li principally reflects variations in water‐rock ratio (w/r) together with a downhole increase of temperature. Seawater flow in the upper volcanic zone is likely to be channeled with generally small but variable w/r ratios. The w/r ratios increase rapidly with depth in the lower volcanic section into the sheeted dike complex indicating water dominated pervasive hydrothermal flow due to intensive upwelling of hydrothermal fluids.

Factors controlling the silicon isotope distribution in waters and surface sediments of the Peruvian coastal upwelling

We present the first systematic study of the silicon isotope composition in the water column (δ30SiSi(OH)4) and in diatoms (δ30Sidiatom) from the underlying surface sediments in a coastal upwelling region. The surface waters upwelling on the shelf off Peru are mainly fed by southward flowing subsurface waters along the coast, which show a mean δ30SiSi(OH)4 of +1.5‰. The concentration of dissolved silicic acid (Si(OH)4) increases towards the south in these waters and with increasing water depth, suggesting lateral mixing with water masses from the south and intense remineralisation of particulate biogenic silica (bSiO2) in the water column and in the surface sediments. Surface waters in the realm of the most intense upwelling between 5°S and 15°S have only marginally elevated δ30SiSi(OH)4 values (δ30SiSi(OH)4=+1.7‰) with respect to the source Si isotope composition, whereas further north and south, where upwelling is less pronounced, surface waters are more strongly fractionated (δ30SiSi(OH)4 up to +2.8‰) due to the stronger utilisation of the smaller amounts of available Si(OH)4. The degree of Si(OH)4 utilisation in the surface waters along the shelf estimated from the Si(OH)4 concentration data ranges from 51% to 93%.The δ30Sidiatom values of hand-picked diatoms in the underlying surface sediments vary from +0.6‰ to +2.0‰, which is within the range of the expected fractionation between surface waters and diatoms. The fractionation signal in the surface waters produced during formation of the diatoms is reflected by the δ30Sidiatom values in the underlying sediments, with the lowest δ30Sidiatom values in the main upwelling region. The silicon isotope compositions of bSiO2 (δ30SibSiO2) from the same surface sediment samples are generally much lower than the δ30Sidiatom signatures indicating a significant contamination of the bSiO2 with biogenic siliceous material other than diatoms, such as sponge spicules. This shift towards lighter δ30SibSiO2 values by up to −1.3‰ compared to δ30Sidiatom signatures for the same surface sediment samples potentially biases the interpretation of δ30Si paleorecords from sediments with low bSiO2 concentrations, and thus the reconstruction of past Si(OH)4 utilisation in surface waters.

Oceanographic drivers of offspring abundance may increase or decrease reproductive variance in a temperate marine fish

In species that reproduce into uncertain environments, the relationship between mean reproductive success (the abundance of new recruits) and the variance in reproductive success (whether adults contribute disproportionally more offspring) may not be straightforward because of stochastic environmental processes that create high variance in reproductive success among adults. In this study, we investigated the relationships between oceanography, reproductive success and reproductive variance in the black rockfish, Sebastes melanops, a long-lived temperate reef fish with pelagic larvae. We quantified black rockfish recruitment, genetic diversity and growth rates from otolith microstructure over 5 years (2005-2009) during which oceanographic conditions differed. We used cross-correlations to determine windows of time during which oceanographic variables were significantly correlated with the resulting abundance or genetic diversity of recruits. We found that warmer ocean temperatures were positively correlated with the abundance of recruits, as well as the effective number of breeders. In contrast, the strength of coastal upwelling during settlement was positively correlated with the annual abundance of new recruits, but was negatively correlated with the effective number of breeders. Larval growth rates were explained substantially more by temperature than by upwelling and suggested that temperature affected survival through growth, while upwelling affected survival through transport. Our results indicated that cold ocean temperatures and intense upwelling caused sweepstakes-like processes to operate on black rockfish populations, despite high abundances of recruits. We propose that a decoupling of the mean and variance in reproductive success may be characteristic of organisms that reproduce into uncertain environments.

Differences in coastal and oceanic SST warming rates along the Canary upwelling ecosystem from 1982 to 2010

Sea surface temperature (SST) trends were calculated for the Moroccan part (22–33°N) of the Canary upwelling ecosystem, which is characterized by permanent upwelling. This analysis was carried out from 1982 to 2010 by means of daily SST data with an approximate spatial resolution of 4×4km.SST trends are not homogeneous either in latitude or longitude. SST trends were observed to increase southward, which can be explained in terms of air temperature (Tair) trends that follow a similar pattern. In addition, remarkable differences in warming trends were observed between coastal and ocean locations at the same latitude (ΔSSTtrend=SSToceantrend−SSTcoasttrend). ΔSSTtrend is positive at most of latitudes showing that the ocean warming rate is higher than the coastal one. The differences between coast and ocean were observed to depend on upwelling index (UI) intensity. Actually, UI calculated for the months with intense upwelling (May–September) showed a no significant positive trend and was significantly correlated (R=0.44; p<0.05) with ΔSST averaged from August to December. In addition, the extended winter EA (December–March) showed a significant correlation (R=0.57; p<0.01) with ΔSST for the months of highest upwelling intensity when a lag of 1yr was considered between both variables.

Distribution du phytoplancton dans les zones d’upwelling de la côte atlantique marocaine située entre les latitudes 32°30′N et 24°N

Marine phytoplankton was studied in January and July 2002 along of four transects: 32°30′N, 29°N, 24°30′N and 24°N. A total of 142 taxa were recorded in this area. The maximal specific richness, both in summer and in winter, was registered around Dakhla (24°N). The global spatiotemporal variability of species richness and specific diversity showed that the most structured and species-rich populations are situated in the coastal areas. The vertical variation of the two parameters showed homogeneity between depth levels. The maximal phytoplanktonic densities are recorded in the southern transects due to the permanent upwelling activity in the southern Atlantic coast. The bathymetric distribution of densities was more heterogeneous during summer, characterized by a high intensity of upwelling. The species Thalassionema nitzschioides, Asterionellopsis glacialis, Melosira, Chaetoceros and Leptocylindrus minimus are indicators of upwelling.

Responses in growth rate of larval northern anchovy (Engraulis mordax) to anomalous upwelling in the northern California Current

AbstractWe examined variability in growth rate during the larval stage of northern anchovy (Engraulis mordax) in response to physical and biological environmental factors in 2005 and 2006. The onset of spring upwelling was anomalously delayed by 2–3 months until mid‐July in 2005; in contrast, spring upwelling in 2006 began as a normal year in the northern California Current. Larval and early juvenile E. mordax were collected in August, September, and October off the coast of Oregon and Washington. Hatch dates ranged from May to September, with peaks in June and August in 2005 and a peak in July in 2006, based on the number of otolith daily increments. Back‐calculated body length‐at‐age in the June 2005 hatch cohort was significantly smaller than in the August 2005 cohort, which had comparable growth to the July 2006 cohort. Standardized otolith daily increment widths as a proxy for seasonal variability in somatic growth rates in 2005 were negative until late July and then changed to positive with intensification of upwelling. The standardized increment width was a positive function of biomass of chlorophyll a concentration, and neritic cold‐water and oceanic subarctic copepod species sampled biweekly off Newport, Oregon. Our results suggest that delayed upwelling in 2005 resulted in low food availability and, consequently, reduced E. mordax larval growth rate in early summer, but once upwelling began in July, high food availability enhanced larval growth rate to that typical of a normal upwelling year (e.g., 2006) in the northern California Current.