Sea Surface Temperature Salinity Research Articles

Reconstruction of Surface Seawater pH in the North Pacific

In the recent significant rise in atmospheric CO2, seawater’s continuous acidification is altering the marine environment’s chemical structure at an unprecedented rate. Due to its potential socioeconomic impact, this subject attracted significant research interest. This study used traditional linear regression, nonlinear regression random forest, and the BP neural network algorithm to establish a prediction model for surface seawater pH based on data of North Pacific sea surface temperature (SST), salinity (SSS), chlorophyll-a concentration (Chl-a), and pressure of carbon dioxide on the sea surface (pCO2) from 1993 to 2018. According to existing research, three approaches were found to be highly accurate in reconstructing the surface seawater pH of the North Pacific. The highest-performing models were the linear regression model using SSS, Chl-a, and pCO2, the random forest model using SST and pCO2, and the BP neural network model using SST, SSS, Chl-a, and pCO2. The BP neural network model outperformed the linear regression and random forest model when comparing the root mean square error and fitting coefficient of the three best models. In addition, the best BP neural network model had substantially higher seasonal applicability than the best linear regression and the best random forest model, with good fitting effects in all four seasons—spring, summer, autumn, and winter. The process of CO2 exchange at the sea–air interface was the key factor affecting the pH of the surface seawater, which was found to be negatively correlated with pCO2 and SST, and positively correlated with SSS and Chl-a. Using the best BP neural network model to reconstruct the surface seawater pH over the North Pacific, it was found that the pH exhibited significant temporal and spatiotemporal variation characteristics. The surface seawater pH value was greater in the winter than the summer, and the pH decline rate over the past 26 years averaged 0.0013 yr−1, with a general decreasing tendency from the northwest to the southeast. The highest value was observed in the tropical western Pacific, while the lowest value was observed in the eastern equatorial region with upwelling, which is consistent with the findings of previous studies.

Using satellite observations of ocean variables to improve estimates of water mass (trans)formation

For the first time, an accurate and complete picture of Mixed Layer (ML) water mass dynamics can be inferred at high spatio-temporal resolution via the material derivative derived from Sea Surface Salinity/Temperature (SSS/T) and Currents (SSC). The product between this satellite derived material derivative and in-situ derived Mixed Layer Depth (MLD) provides a satellite based kinematic approach to the water mass (trans)formation framework (WMT/F) above ML. We compare this approach to the standard thermodynamic approach based on air-sea fluxes provided by satellites, an ocean state estimate and in-situ observations. Southern Hemisphere surface density flux and water mass (trans)formation framework (WMT/F) were analysed in geographic and potential density space for the year 2014. Surface density flux differences between the satellite derived thermodynamic and kinematic approaches and ECCO (an ocean state estimate) underline: 1) air-sea heat fluxes dominate variability in the thermodynamic approach; and 2) fine scale structures from the satellite derived kinematic approach are most likely geophysical and not artefacts from noise in SSS/T or SSC—as suggested by a series of smoothing experiments. Additionally, ECCO revealed surface density flux integrated over ML are positively biased as compared to similar estimates assuming that surface conditions are homogeneous over ML—in part owing to the e-folding nature of shortwave solar radiation. Major differences between the satellite derived kinematic and thermodynamic approaches are associated to: 1) lateral mixing and mesoscale dynamics in the kinematic framework; 2) vertical excursions of, and vertical velocities through the ML base; and 3) interactions between ML horizontal velocities and ML base spatial gradients.

Effects of Water Masses and Circulation on the Surface Water Partial Pressure of Carbon Dioxide in Summer in Eastern Beibu Gulf, China

A gulf is a typical ecological zone where carbon cycle is jointly affected by complex environmental factors and strong human activities, and the Beibu Gulf has complex water masses and circulation structures. In this study, we used underway, continuous observational data of the surface water partial pressure of carbon dioxide (pCO2), temperature (SST), salinity (SSS), dissolved oxygen (DO), and chlorophyll α along with vertical profile observations of temperature, salinity, carbonate system parameters and nutrients to determine the spatiotemporal variations and research effects of water masses and circulation on summer pCO2 in the eastern part of Beibu Gulf. In the summers of 2011 and 2014, the mean pCO2 in the eastern part of Beibu Gulf was 417 μatm and 405 μatm, respectively, and the mean sea–air CO2 flux was 3.3 mmol m−2 d−1 and 1.6 mmol m−2 d−1, respectively. In the summer of 2011, the northern part of the Beibu Gulf was controlled by a cyclonic circulation, and pCO2 at the center of the cyclonic circulation increased by more than 15 μatm to a mean value of more than 10 μatm above that of the surrounding waters. The southern part of the Beibu Gulf was affected by an anticyclonic circulation and western coastal water masses, with a high temperature, low salinity, low pCO2, and downwelling surface waters. In the summer of 2011, the mean pCO2 was approximately 17 μatm lower than that in the surrounding waters, and no clear downwelling was observed in summer 2014. The eastern part of Beibu Gulf was a source of atmospheric CO2 in the summer, only the region affected by the northern coastal water in the eastern part of Beibu Gulf was a sink of atmospheric CO2, and pCO2 had distinctly different spatiotemporal distributions under the influence of complex water masses and circulation structures.

Spatial and temporal variability of the physical, carbonate and CO2 properties in the Southern Ocean surface waters during austral summer (2005-2019)

In situ measurements of sea surface temperature (SST), salinity (SSS), Total Alkalinity (AT) and Total Carbon (CT) were obtained during austral summer (mid-February to mid-March) from 2005 to 2019 in the Southern Ocean (SO), along a transect between Hobart, Tasmania and Dumont d’Urville French Antarctic Station. The studied transect is divided in four regions from North to South: the Subtropical Zone (STZ), the Subantarctic Region (SAR), the Antarctic Region (AAR) and the Coastal Antarctic Zone (CAZ). Latitudinal distribution of measured SST, SSS, AT, CT as well as calculated pH, CO2 parameters (seawater fugacity of CO2 (fCO2sw), difference between seawater and atmospheric fCO2 (ΔfCO2), CO2 flux (FCO2)) and satellite-derived Chlorophyll a (Chl-a) are discussed. We show that the variability of physical and carbonate parameters in the STZ and north of the SAR are related to the mesoscale activity. In the CAZ, the freshwater inputs from sea-ice melting strongly impact the variability of all parameters. The comparison between physical and carbonate parameters highlights that AT and CT are directly related to the latitudinal variability of SST and SSS. Study of the CO2 parameters shows that the transect is a sink of CO2 during February and March, with a mean FCO2 of −4.0 ± 2.8 mmol m−2 d−1. The most negative values of FCO2 are found in the STZ and SAR north of 50°S and in the AAR south of 62°S, where biological activity is high. New simple empirical relationships are developed for AT from SST and SSS and for CT using SST, SSS and atmospheric fCO2 (fCO2atm) for the austral summer in the studied area. Using high resolution SSS and SST from the SURVOSTRAL program, trends of AT and CT are determined in the SAR and the AAR from 2005 to 2019. SST, SSS and AT increase over this period in the SAR, which might be explained by the southward migration of the Subtropical Front. In the AAR, no clear trend is detected. CT increases by 1.0 ± 0.2 and 0.8 ± 0.3 μmol kg−1 yr−1 in the SAR and AAR respectively. The trend in the AAR is attributed to the increase in anthropogenic CO2 emissions in the atmosphere while, in the SAR, hydrographic changes also contribute to the increase. Using the coefficient associated with fCO2atm in the equation of CT, we estimate the impact of atmospheric CO2 increase on CT at 1.18 ± 0.14 μmol kg−1 yr−1 and 1.07 ± 0.13 μmol kg−1 yr−1 in the SAR and AAR respectively. Decreases in pH are observed in both regions (−0.0018 ± 0.0001 and −0.0026 ± 0.0003 yr−1 in the SAR and AAR respectively), indicating the sensitivity of surface waters in the area towards the development of ocean acidification processes under rising anthropogenic emissions.

The sub-fossil diatom distribution in the Beibu Gulf (northwest South China Sea) and related environmental interpretation.

Located in northwestern South China Sea (SCS), the Beibu Gulf constitutes an environmentally sensitive region shaped by land-ocean-atmosphere interactions in Asia between the western Pacific and eastern Indian Oceans. This study aims to provide a comprehensive view of the sub-fossil diatom biogeography, distribution pattern and oceanographic environmental controls with support of multivariate methods based on Beibu Gulf core-top samples. Cluster analysis of diatom assemblages divides the distribution pattern into four subclusters. Sea surface salinity (SSS), temperature (SST), trophic state (chlorophyll a concentration in this study) and water depth constrain the diatom distribution pattern through canonical redundancy analysis although only partly support an interpretation of the relationship between these various variables. Chlorophyll a has a strong correlation to diatom distribution, and responds to Paralia sulcata occurrence, while SSS and SST also have significant influence and indicate warm water invasion from the open SCS. Water depth is a subordinate factor in terms of Beibu Gulf diatom distribution. The ca. 25 m water-depth marks the upper extent of Paralia sulcata dominance in the northern Beibu Gulf. A strong mixing area with a complex diatom distribution exists below this water depth in the middle of Beibu Gulf. Coastal currents from north of SCS invade Beibu Gulf through Qiongzhou Strait and south of Hainan Island, as recorded by higher percentages of Paralia sulcata and Cyclotella striata at these sites. Our results provide a selection of evaluation method for a marine ecological red-line definition for sustainable development. This study highlights the perspective relationships between the spatial distribution of sub-fossil diatom assemblages in surface sediments and oceanographic variables, which could serve as a model for paleoenvironmental and paleoclimatic reconstruction in future marginal sea geoscience research for the Beibu Gulf, northwestern SCS.

Similarities and Contrasts in Time-Mean Striated Surface Tracers in Pacific Eastern Boundary Upwelling Systems: The Role of Ocean Currents in Their Generation

Eastern boundary upwelling systems feature strong zonal gradients of physical and biological properties between cool, productive coastal oceans and warm, oligotrophic subtropical gyres. Zonal currents and jets (striations) are therefore likely to contribute to the transport of water properties between coastal and open oceanic regions. For the first time, multi-sensor satellite data are used to characterize the time-mean signatures of striations in sea surface temperature (SST), salinity (SSS), and chlorophyll-a (Chl-a) in subtropical eastern North/South Pacific (ENP/ESP) upwelling systems. In the ENP, tracers exhibit striated patterns extending up to ~2500 km offshore. Striated signals in SST and SSS are highly correlated with quasi-zonal jets, suggesting that these jets contribute to SST/SSS mesoscale patterns via zonal advection. Striated Chl-a anomalies are collocated with sea surface height (SSH) bands, a possible result of mesoscale eddy trains trapping nutrients and forming striated signals. In the ESP, the signature of striations is only found in SST and coincides with the SSH bands, consistently with quasi-zonal jets located outside major zonal tracer gradients. An interplay between large-scale SST/SSS advection by the quasi-zonal jets, mesoscale SST/SSS advection by the large-scale meridional flow, and eddy advection may explain the persistent ENP hydrographic signature of striations. These results underline the importance of quasi-zonal jets for surface tracer structuring at the mesoscale.

Interannual Variability of the Lena River Plume Propagation in 1993–2020 during the Ice-Free Period on the Base of Satellite Salinity, Temperature, and Altimetry Measurements

The Lena River plume significantly affects the thermohaline, optical and chemical properties of the eastern Arctic seas. We use sea surface salinity (SSS), temperature (SST), and altimetry measurements to study features of the Lena plume propagation during 1993–2020. A comparison of Soil Moisture Active Passive (SMAP) SSS measurements with in situ data obtained using the flow-through system in oceanographic surveys in 2018–2019 demonstrates good coincidence with correlation ~ 0.96 and RMSD ~ 1 psu. The SMAP data were used to reconstruct the plume evolution in 2015–2020 and to identify three main types of Lena plume propagation, which are mainly related to the variability of dominant zonal wind direction: «northern»—the plume moves to the north from the delta up to 78° N; «eastern»—the plume moves eastward along the Siberian coast up to 180° E; «mixed» between two main types. Brackish plume waters were characterized by increased temperature and sea level, which provides the opportunity for studying the Lena plume dynamics using satellite altimetry and infrared measurements. These data were analyzed to study the interannual variability of plume propagation during the ice-free period of 1993–2020. The obtained results show that the «northern» type is observed twice more often than the «eastern» one, but the «eastern» type has intensified since 2010.

Air-sea CO2 flux in an equatorial continental shelf dominated by coral reefs (Southwestern Atlantic Ocean)

Coral reefs are ecosystems highly vulnerable to changes in seawater carbonate chemistry, including those related to the ocean acidification and global warming. Brazilian coral reefs contains the major area of reefs coverage in the Southwestern (SW) Atlantic Ocean, however, studies aimed at investigating the controls of seawater carbonate chemistry in coral reefs are still overlooked in Brazil. This study comprehends the first investigation of complete seawater carbonate chemistry parameters in a section of the equatorial continental shelf dominated by coral reefs in the SW Atlantic Ocean. The sampling included spatial continuous underway measurements of sea surface CO2 fugacity (fCO2sw), temperature (SST), salinity (SSS), and discrete investigations of total alkalinity (TA), dissolved inorganic carbon (DIC), bicarbonate (HCO3-), carbonate (CO32−), and saturation state of aragonite (Ωara). The study was conducted during a dry period (July-2019) in the Marine State Park of Pedra da Risca do Meio (PRM), a marine protected area dominated by coral reef communities. Overall, the coral-reef dominated waters presented higher values of fCO2sw (475 ± 28 μatm), and lower values of pHT (7.98 ± 0.008), CO32− (217 ± 5 μmol kg-1) and Ωara (3.49 ± 0.07), compared to nearshore regions without the influence of coral reef waters, where the averages of fCO2sw, pHT, CO32−, and Ωarawere, respectively, 458 ± 21 μatm, 8.00 ± 0.007, 224 ± 4 μmol kg-1, and 3.58 ± 0.05. The relationship between salinity-normalized TA (nTA) and salinity-normalized DIC (nDIC) showed a slope higher than 1 (1.26) in the coral reef, evidencing the occurrence of calcium carbonate (CaCO3) precipitation and prevalence of inorganic carbon metabolism. The CaCO3 precipitation involves the consumption of TA and DIC in a ratio 2:1, with production of CO2. This mechanism explains the higher values of fCO2sw in the coral reef-dominated waters. The values of fCO2sw were always higher than the atmospheric values (fCO2air), indicating a permanent source of CO2 in the study area during the sampled period. The calculated fluxes of CO2 at the air-sea interface averaged 8.4 ± 6.5 mmolC m-2 d-1 in the coral reef-dominated waters, and these data are higher than those verified in nearshore and offshore locations. These higher emissions of CO2 in coral reef-dominated waters evidence that the carbon budgets calculated for North and Northeastern continental shelf of Brazil must include these environments taking into account the widespread coral reef coverage in the region. This study also confirms that biogeochemical processes occurring in coral reefs are modifying the seawater carbonate chemistry, with implication in the context of the current process of ocean acidification.

Wintertime fCO2 Variability in the Subpolar North Atlantic Since 2004

AbstractWinter data of surface ocean temperature (SST), salinity (SSS) and CO2 fugacity (fCO2) collected on the VOS M/V Nuka Arctica in the subpolar North Atlantic between 2004 and 2017 are used to establish trends, drivers, and interannual variability. Over the period, waters cooled and freshened, and the fCO2 increased at a rate similar to the atmospheric CO2 growth rate. When accounting for the freshening, the inferred increase in dissolved inorganic carbon (DIC) was found to be approximately twice that expected from atmospheric CO2 alone. This is attributed to the cooling. In the Irminger Sea, fCO2 exhibited additional interannual variations driven by atmospheric forcing through winter mixing. As winter fCO2 in the region is close to the atmospheric, the subpolar North Atlantic has varied between being slightly supersaturated and slightly undersaturated over the investigated period.

Species composition and assemblages of ichthyoplankton during summer in the East China Sea

The East China Sea (ECS) is one of the most important fish spawning and nursery grounds in the north Pacific. Even though summer is an important spawning season for many fishes in the region, large-scale molecular identification studies on ichthyoplankton during this season are few. In this study, we sampled 8,933 fish eggs and 12,161 fish larvae from 25 stations during the summer of 2009. Using DNA barcoding, a number of the fish eggs and larvae were identified and classified into 45 and 124 taxa, respectively. Principal component analysis (PCA) categorized the inshore stations of the Changjiang Diluted Water area as having the hydrographic features of low sea surface temperature (SST), salinity (SSS) and high chlorophyll a (SSC) contents, whereas the continental shelf and offshore stations under the influence of the Kuroshio Current displayed the opposite results. Ichthyoplankton was more abundant at the inshore stations than the offshore stations, but species diversity was lower at the former locations. Species compositions of both fish eggs and fish larvae at the 25 stations were categorized into three different assemblages based on a non-metric multidimensional scaling analysis. Combining the assemblage patterns of ichthyoplankton with the results of the PCA and satellite images of SST and SSC showed that the assemblage patterns of fish eggs were correlated with water mass, while those of the fish larvae were not.

Growth variability of Pacific saury Cololabis saira larvae under contrasting environments across the Kuroshio axis: survival potential of minority versus majority

AbstractGrowth variability was examined for Pacific saury Cololabis saira larvae under contrasting environments across the Kuroshio axis, based on samples collected during the winter spawning season in 2013 and 2014. The growth rate index (residual of the otolith marginal 3‐day mean increment width from the linear regression on knob length) of larvae was compared among three areas: the inshore side of the Kuroshio axis, the Kuroshio axis, and the offshore side of the Kuroshio axis in relation to sea surface temperature (SST), salinity (SSS) and chlorophyll‐a (CHL) concentration. The larvae were more densely distributed in the Kuroshio axis and offshore areas of higher temperature and salinity and lower chlorophyll‐a concentration than in the inshore areas of lower temperature and salinity and higher chlorophyll‐a concentration. No marked differences in the growth rate index were found among the three areas, even though the larvae in the inshore areas showed slightly higher growth rates in 2013. Despite the broad ranges of environmental factors, no clear relationship between the growth rate index and any environmental factor was detected. The survival potential of Pacific saury larvae was considered to be at least comparable under contrasting environments across the Kuroshio axis. Such a geographical homogeneity is concluded to be attributable to compensable effects of physical and biological factors. We hypothesize that the minority under physically‐unfavorable but biologically‐favorable conditions on the inshore side of the Kuroshio axis could survive equally well as the majority under physically‐favorable but biologically‐unfavorable conditions around the Kuroshio axis and on the offshore side of the Kuroshio axis.

Occurrence and density of Pacific saury Cololabis saira larvae and juveniles in relation to environmental factors during the winter spawning season in the Kuroshio Current system

AbstractThe occurrence and density of Pacific saury Cololabis saira larvae and juveniles were examined in relation to environmental factors during the winter spawning season in the Kuroshio Current system, based on samples from extensive surveys off the Pacific coast of Japan in 2003–2012. Dense distributions of larvae and juveniles were observed in areas around and on the offshore side of the Kuroshio axis except during a large Kuroshio meander year (2005). The relationships of larval and juvenile occurrence and density given the occurrence to sea surface temperature (SST), salinity (SSS), and chlorophyll‐a concentration (CHL) were examined by generalized additive models for 10‐mm size classes up to 40 mm. In general, the optimal SST for larval and juvenile occurrence and density given the occurrence was consistently observed at 19–20°C. The patterns were more complex for SSS, but a peak in occurrence was observed at 34.75–34.80. In contrast, there were negative relationships of occurrence and density given the occurrence to CHL. These patterns tended to be consistent among different size classes, although the patterns differed for the smallest size class depending on environmental factors. Synthetically, the window for spawning and larval and juvenile occurrence and density seems to be largely determined by physical factors, in particular temperature. The environmental conditions which larvae and juveniles encounter would be maintained while they are transported. The survival success under the physically favorable but food‐poor conditions of the Kuroshio Current system could be key to their recruitment success.

Potential fish habitat mapping using MODIS-derived sea surface salinity, temperature and chlorophyll-a data: South China Sea Coastal areas, Malaysia

This paper demonstrates the use of moderate resolution imaging spectro-radiometer (MODIS) data for fish forecasting mapping of seasonal spatial distribution of sea surface salinity (SSS), temperature (SST) and chlorophyll-a in the ocean waters off the coast of Semporna, Malaysia. Multi-linear regression analysis was performed to estimate SSS and the Brown and Minnet algorithm was used for the SST. The extracted parameters were validated using in situ measurement taken with Hydro-Lab equipment. The extracted parameters from MODIS images reveal the signature values which establish the relationships between these parameters, and thus delineating the potential fish zonation (PFZ) map. These developed models will help for accurate monitoring of large coverage areas at low cost and within short period of time. Furthermore, such models will allow the prediction of the total fish catch in different seasons, thus contributing to fish industry management and marketing. This research recommends the use of PFZ map for mass scale fish harvesting in short time for larger areas. Finally, the research has developed a potential fish zone model amalgamating all the above parameters. The PFZ mapping was carried out off the coast of Semporna, Sabah as there were sufficient fish catch data for accuracy assessment. The R was computed as 0.93 and the higher fish catch areas have coincided very well with the higher PFZ values, meaning the tool is ready for use for operational near real-time fish forecasting.

Seasonal and Inter-Annual Variations in pCO2sea and Air-Sea CO2 Fluxes in Mid-Latitudes of the Western and Eastern North Pacific during 1999-2006: Recent Results Utilizing Voluntary Observation Ships

We have investigated the seasonal and inter-annual variations of the difference in partial pressure of CO2 between surface seawater (pCO2sea) and overlying air (pCO2air) and the air-sea CO2 flux in the mid-latitudes of the western North Pacific (WNP; 25-40°N, 140-170°E) and eastern North Pacific (ENP; 25-40°N, 120-150°W) from 1999 to 2006 using the latest voluntary observation ship data. In the WNP and ENP, the area-averaged ΔpCO2 (pCO2air-pCO2sea) was at its minimum in late summer (-4.6 to 6.7 µatm in the WNP and -32.5 to -20.5 µatm in the ENP) and at its maximum in late winter (51.0 to 59.8 µatm in the WNP and 35.1 to 46.2 µatm in the ENP). The WNP acts as a moderate sink for atmospheric CO2 (4.1 to 5.5 mmol m-2d-1), while the ENP acts as a weak sink (1.1 to 1.9 mmol m-2d-1). Because ΔpCO2 is mainly controlled by pCO2sea, we have evaluated the effect of the factors controlling pCO2sea: sea surface temperature (SST), salinity (SSS), dissolved inorganic carbon (TCO2), and total alkalinity (AT). In the WNP, not only SST but also TCO2 plays an important role in the seasonal pCO2sea variation, while the SST could only explain most of the pCO2sea variation in the ENP. From 1999 to 2006, pCO2sea increased at a significantly lower rate (0.53 ± 0.11 µatm yr-1) than pCO2air (1.81 ± 0.01 µatm yr-1) in the WNP, and at a slightly lower rate in the ENP (1.32 ± 0.16 µatm yr-1). The air-sea CO2 flux increased at a rate of 0.19 ± 0.05 mmol m-2d-1 yr-1 in the WNP and 0.09 ± 0.03 mmol m-2d-1 yr-1 in the ENP, suggesting that the WNP is a stronger sink for atmospheric CO2.

Prediction of surface ocean pCO2 from observations of salinity, temperature and nitrate: The empirical model perspective

This paper evaluates whether a thermodynamic ocean-carbon model can be used to predict the monthly mean global fields of the surface-water partial pressure of CO2 (pCO2SEA) from sea surface salinity (SSS), temperature (SST), and/or nitrate (NO3) concentration using previously published regional total inorganic carbon (CT) and total alkalinity (AT) algorithms. The obtained pCO2SEA values and their amplitudes of seasonal variability are in good agreement with multi-year observations undertaken at the sites of the Bermuda Atlantic Timeseries Study (BATS) (31°50’N, 60°10’W) and the Hawaiian Ocean Time-series (HOT) (22°45’N, 158°00’W). By contrast, the empirical models predicted CT less accurately at the Kyodo western North Pacific Ocean Time-series (KNOT) site (44°N, 155°E) than at the BATS and HOT sites, resulting in greater uncertainties in pCO2SEA predictions. Our analysis indicates that the previously published empirical CT and AT models provide reasonable predictions of seasonal variations in surface-water pCO2SEA within the (sub) tropical oceans based on changes in SSS and SST; however, in high-latitude oceans where ocean biology affects CT to a significant degree, improved CT algorithms are required to capture the full biological effect on CT with greater accuracy and in turn improve the accuracy of predictions of pCO2SEA.

Spawning areas and larval distributions of anchovy <em>Engraulis encrasicolus</em> in relation to environmental conditions in the Gulf of Tunis (Central Mediterranean Sea)

Early life stages of anchovy were investigated in the Gulf of Tunis by means of four seasonal surveys carried out from summer 2002 to spring 2003. Anchovy eggs and larvae were found all year round, but they were much more abundant in spring and summer. In spring, the main spawning area was located in the north of the Gulf, to the west and southwest of Zembra Island. In summer, higher egg and larva abundances were also observed to the southwest of Zembra Island, but secondary spawning grounds were detected in the vicinity of the mouths of the Rivers Majreda and Meliane. No direct correlations between sea surface temperature (SST), salinity (SSS) and chlorophyll a and the horizontal distribution of eggs and larvae were observed. However, egg distributions in all seasons and larval distributions in summer and autumn were significantly related to depth. The temporal variation of temperature seems to control the spawning intensity and the beginning of spawning seems to be triggered by the increase in SST.

Increased coastal upwelling in the California Current System

State‐space statistical models are applied to long environmental time series of monthly northward wind stress, sea surface temperature (SST), salinity (SSS), and sea level (SL) from the west coast of North America. The models use a combination of Kalman filtering and maximum likelihood methods, which estimate a nonlinear trend, a nonstationary and nondeterministic seasonal signal, and an autoregressive term, and effectively separate the seasonal signals from the long‐term trends. The seasonal series are examined for behavior consistent with increasing coastal upwelling during the spring‐summer upwelling “season,” presumably in response to a pattern of long‐term global warming. Over a region of the California Current System (CCS) where coastal upwelling is a dominant process (32–40°N), wind stress, SST, SSS, and SL all show strong evidence of a systematic intensification of upwelling during April–July. Model trend series suggest a linear tendency for increasing equatorward stress (in agreement with the seasonal tendency), but warmer SST (opposite the seasonal and the expectation of greater upwelling). The linear tendencies of the SST and stress trends are generally an order of magnitude greater than the seasonal tendencies. Thus the long‐term trend in SST masks the cooling effect of increased seasonal upwelling, and the trend in equatorward stress suggests an artificially large seasonal increase in the observed spring and summer stress. A key to identifying these patterns has been the ability to separate the long‐term nonlinear trend, using the state‐space models, which mask the signal of increased upwelling in the observations.