Autumn Cruises Research Articles

Size-fractioned zooplankton biomass in the Barents Sea: macroecological patterns across biogeography, climate, and varying ecosystem state (1989-2020)

The zooplankton community in the Barents Sea was monitored during autumn cruises from 1989-2020, with biomass determined as the depth-integrated dry weight (g m-2) of 3 size fractions (>2 mm, 1-2 mm, <1 mm). A large data set of 4543 sampling stations encompassing a subdivision of the Barents Sea was spatially averaged into 15 polygons based on topography. The resulting data set is used to describe relationships between the biomass of size fractions as expressions of the size structure of the zooplankton communities. Each of the 3 size fractions was positively related to the total zooplankton biomass (sum of fractions). The medium size fraction, which contained on average 48% of the total biomass, showed a strong linear correlation with total biomass (R2 ≈ 0.8). The medium fraction contained the older copepodite stages of Calanus species (C. finmarchicus and C. glacialis), which are dominant species interpreted to drive the overall changes in zooplankton biomass. The biomass of the small size fraction decreased with decreasing total biomass, but less so than the medium fraction. Thus, the small/medium biomass ratio increased as the total biomass decreased. This trend was most pronounced for shallow and central polygons, which coincide with the core feeding area of the large Barents Sea stock of capelin Mallotus villosus. The change in the small/medium biomass ratio is interpreted to reflect a shift from Calanus to smaller zooplankton in response to predation by capelin and other planktivorous predators, and possibly also by warming due to climate change.

Characteristics, seasonal variations, and dry deposition fluxes of carbonaceous and water-soluble organic components in atmospheric aerosols over China's marginal seas

A total of 37 atmospheric aerosol samples were collected over the Yellow and Bohai Seas (YBS) during four cruises in autumn, winter, spring and summer from 2017 to 2018. The concentrations of organic carbon (OC) and water-soluble organic carbon (WSOC) ranged from 1.04 to 15.43 μg m−3 and 0.77–5.49 μg m−3, respectively, with higher values in autumn and winter than in spring and summer. WSOC contributed 68.49 % to OC in summer and 34.55 % in winter and was affected by temperature and relative humidity. Dicarboxylic acid showed a predominance of oxalic acid followed by malonic and then succinic acids. The contributions of secondary sources to OC and WSOC were 54 % and 65.3 %, respectively, indicating the importance of secondary aging in improving the water solubility of OC. The dry deposition flux of WSOC over the YBS was estimated to be 0.87 mg m−2 d−1, which might play a potential role in the marine carbon cycle.

Size-fractioned zooplankton biomass in the Barents Sea ecosystem: changes during four decades of warming and four capelin collapses (1980–2020)

Abstract Zooplankton in the Barents Sea has been monitored by the Institute of Marine Research in Norway on autumn cruises since 1986, using a standardized procedure with determination of dry weight biomass in three size fractions following splitting of the sample in two halves. Along with summer data for the early 1980s, we can now describe changes of zooplankton biomass over four decades. The biomass of the central Barents Sea has fluctuated inversely with collapses and recoveries of the Barents Sea capelin stock, which is a major planktivore. Zooplankton biomass in the central Barents Sea was low in 1983 and 1984, driven by low abundance of Calanus finmarchicus, followed by a pronounced peak in 1987 associated with a “first” collapse of the capelin stock. Biomass showed another pronounced peak in 1994, driven by the small size fraction and interpreted to reflect an advective signal from the adjacent Norwegian Sea. In the two most recent decades, there have been divergent trends, with a relatively high biomass in the inflowing Atlantic water, reflecting a second summer generation of C. finmarchicus, and decreased biomass in the central area, reflecting a lower abundance of Calanus glacialis driven by a combined effect of capelin predation and climate.

Planktonic foraminiferal assemblages reflect warming during two recent mid-latitude marine heatwaves

Under future climate scenarios, ocean temperatures that are presently extreme and qualify as marine heatwaves (MHW) are forecasted to increase in frequency and intensity, but little is known about the impact of these events on one of the most common paleoproxies, planktonic foraminifera. Planktonic foraminifera are globally ubiquitous, shelled marine protists. Their abundances and geochemistry vary with ocean conditions and fossil specimens are commonly used to reconstruct ancient ocean conditions. Planktonic foraminiferal assemblages are known to vary globally with sea surface temperature, primary productivity, and other hydrographic conditions, but have not been studied in the context of mid-latitude MHWs. For this study, the community composition and abundance of planktonic foraminifera were quantified for 2010-2019 along the Newport Hydrographic Line, a long-term monitoring transect at 44.6°N in the Northern California Current (NCC). Samples were obtained from archived plankton tows spanning 46 to 370 km offshore during annual autumn (August – October) cruises. Two MHWs impacted the region during this timeframe: the first during 2014-2016 and a second, shorter duration MHW in 2019. During the 2014-2016 MHW, warm water subtropical and tropical foraminifera species were more prevalent than the typical polar, subpolar, and transitional species common to this region. Cold water species were abundant again after the first MHW dissipated in late 2016. During the second, shorter-duration MHW in 2019, the assemblage consisted of a warm water assemblage but did not include tropical species. The foraminiferal assemblage variability correlated with changes in temperature and salinity in the upper 100 meters and was not correlated with distance offshore or upwelling. These results suggest that fossil foraminiferal assemblages from deep sea sediment cores may provide insight into the magnitude and frequency of past MHWs.

Phytoplankton biomass and photophysiology at the sub-Antarctic Prince Edward Islands ecosystem in the Southern Ocean

At the sub-Antarctic Prince Edward Islands (PEIs), a diverse ecosystem is supported by enhanced phytoplankton biomass levels, commonly referred to as the island mass effect. Phytoplankton responses to varied environmental conditions during austral summer (December 2008) and autumn (April–May 2013–2018) cruises were characterised by both surface and subsurface chlorophyll a (chla) maxima. While subsurface chla maxima were generally near the base of the upper mixed layer (z uml ) during the summer cruise, such maxima were located well below z uml during autumn cruises. Non-photochemical quenching resulted in severe underestimation of surface in situ chla. Substantially low F v /F m and σ PSII in the surface layers during December 2008 confirmed the photoinhibitory effects of high light exposure during the day and suggested damage to phytoplankton photosystem II reaction centres. Physiological measurements revealed that phytoplankton communities were probably not limited by nitrate or iron. However, some nutrient stress may have resulted from low surface silicates, which showed comparatively more daytime depletion during December 2008 than April–May 2013–2015. While the spatial distribution of in situ phytoplankton biomass during December 2008 was reminiscent of the island mass effect, congruent satellite observations surprisingly revealed that chla in the open ocean surrounding the PEIs was in fact much higher than chla on the island shelf. Our findings suggested that upwelling and retention, and consequent phytoplankton biomass accumulation, usually associated with a Taylor column structure at the PEIs may have been disrupted by enhanced offshore advection stemming from the interaction of mesoscale eddies and fronts with the PEI shelf. However, more detailed investigations are required to properly understand the spatial and temporal variations of phytoplankton biomass and their physiological responses to environmental fluctuations. • Surface and subsurface chlorophyll a maxima were observed in summer and autumn. • In December 2008, these maxima were located near the base of the upper mixed layer. • During autumn 2013–2018, such maxima were well below the upper mixed layer. • Several daytime profiles were compromised by non-photochemical quenching. • Photophysiological parameters confirmed effects of daytime high light exposure.

Phenology and Environmental Control of Phytoplankton Blooms in the Kong Håkon VII Hav in the Southern Ocean

Knowing the magnitude and timing of pelagic primary production is important for ecosystem and carbon sequestration studies, in addition to providing basic understanding of phytoplankton functioning. In this study we use data from an ecosystem cruise to Kong Håkon VII Hav, in the Atlantic sector of the Southern Ocean, in March 2019 and more than two decades of satellite-derived ocean color to study phytoplankton bloom phenology. During the cruise we observed phytoplankton blooms in different bloom phases. By correlating bloom phenology indices (i.e., bloom initiation and end) based on satellite remote sensing to the timing of changes in environmental conditions (i.e., sea ice, light, and mixed layer depth) we studied the environmental factors that seemingly drive phytoplankton blooms in the area. Our results show that blooms mainly take place in January and February, consistent with previous studies that include the area. Sea ice retreat controls the bloom initiation in particular along the coast and the western part of the study area, whereas bloom end is not primarily connected to sea ice advance. Light availability in general is not appearing to control the bloom termination, neither is nutrient availability based on the autumn cruise where we observed non-depleted macronutrient reservoirs in the surface. Instead, we surmise that zooplankton grazing plays a potentially large role to end the bloom, and thus controls its duration. The spatial correlation of the highest bloom magnitude with marked topographic features indicate that the interaction of ocean currents with sea floor topography enhances primary productivity in this area, probably by natural fertilization. Based on the bloom timing and magnitude patterns, we identified five different bloom regimes in the area. A more detailed understanding of the region will help to highlight areas with the highest relevance for the carbon cycle, the marine ecosystem and spatial management. With this gained understanding of bloom phenology, it will also be possible to study potential shifts in bloom timing and associated trophic mismatch caused by environmental changes.

Upper Ocean Stratification in the Eastern Pacific During the SPURS‐2 Field Campaign

AbstractThe region between a shallow mixed layer and a deep isothermal layer resulting from salinity stratification is called a barrier layer (BL). Since BLs hinder the surface heat and momentum exchange with the ocean subsurface, they play an important role in air‐sea interaction. Synoptic features and formation of BLs and associated temperature inversions (TIs) in the Eastern Pacific Fresh Pool (EPFP) were investigated using shipboard observations. BLs and TIs were found in the high‐precipitation EPFP, a frontal transition zone (FTZ) and in the sea surface salinity (SSS) front during a 2016 boreal summer cruise. During a 2017 boreal autumn cruise, BLs and TIs were found from the southern part of the EPFP to the SSS front. The BLs in the SSS front and the FTZ were meridionally displaced from the precipitation maximum during both the 2016 and 2017 cruises. Freshening and cooling by tilting of both the isohalines and isotherms of the SSS front occurred via Ekman and geostrophic flow during both cruises, and also within the EPFP during 2016. The SSS front was a dominant contributor to the density gradient in the horizontal plane. A high dissolved oxygen content observed within BLs confirmed that the surface flow plays an important role in the BL and TI formation through the tilting process. Patchy distribution of freshening and cooling by tilting implies an intermittent BL and TI formation with short time scales.

Community assembly of bacteria and archaea in coastal waters governed by contrasting mechanisms: A seasonal perspective.

Marine planktonic bacteria and archaea commonly exhibit pronounced seasonal succession in community composition. But the existence of seasonality in their assembly processes and between-domain differences in underlying mechanism are largely unassessed. Using a high-coverage sampling strategy (including single sample for each station during four cruises in different seasons), 16S rRNA gene sequencing, and null models, we investigated seasonal patterns in the processes governing spatial turnover of bacteria and archaea in surface coastal waters across a sampling grid over ~300km in the East China Sea. We found that archaea only bloomed in prokaryotic communities during autumn and winter cruises. Seasonality mostly overwhelmed spatial variability in the compositions of both domains. Bacterial and archaeal communities were dominantly governed by deterministic and stochastic assembly processes, respectively, in autumn cruise, probably due to the differences in niche breadths (bacteria<archaea) and relative abundance (bacteria>archaea). Stochasticity dominated assembly mechanisms of both domains but was driven by distinct processes in winter cruise. Determinism-dominated assembly mechanisms of bacteria rebounded in spring and summer cruises, reflecting seasonal variability in bacterial community assembly. This could be attributed to seasonal changes in bacterial niche breadths and habitat heterogeneity across the study area. There were seasonal changes in environmental factors mediating the determinism-stochasticity balance of bacterial community assembly, holding a probability of the existence of unmeasured mediators. Our results suggest contrasting assembly mechanisms of bacteria and archaea in terms of determinism-vs.-stochasticity pattern and its seasonality, highlighting the importance of seasonal perspective on microbial community assembly in marine ecosystems.

Life history of an anticyclonic eddy in the Algerian basin from altimetry data, tracking algorithm and in situ observations.

Abstract Frequently-forming long-life mesoscale eddies are observed in the Algerian Basin that influence the circulation of the wider Western Mediterranean Sea. Most of these structures store and transport water masses including associated physical and biological properties throughout the entire basin. In order to study the evolution of a long-life anticyclonic eddy, we use a multiplatform approach based on remote sensing data analysis and in situ measurements. We present a case study of an anticyclonic eddy that persisted for 17 months within the basin. The feature was identified through a hybrid method of eddy detection and tracking applied to altimetry data, and sampled twice during two different oceanographic cruises in autumn 2004 and late spring 2005. Transect observations of potential temperature, salinity, density and the dissolved oxygen concentration were utilised to infer water mass properties and eddy characteristics. In situ data show that water of Atlantic origin, initially trapped by the eddy during its formation, was modified during the eddy lifetime. The time evolution of radius, kinetic energy and vorticity suggests dividing the eddy lifetime into three phases: the eddy formation, an intermediate period of high variability and a final, lower energy phase. The track followed by the eddy confirms the hypothesis of an interaction with the North Balearic Front and a consequent change of the eddy's physical properties. Decomposing the eddy's kinetic energy into mean and fluctuating terms allows us to describe its interaction with the mean circulation of the basin. In particular during formation, the southern part of the eddy absorbs energy from the mean circulation, while it provides energy to the mean flow in its northern part. In the second phase, when the eddy is far from the coast, it receives energy from the mean flow. Combining in situ data analysis with the results of the satellite-imagery-based detection and tracking method has proven to be a very useful method in assessing the evolution of a mesoscale structure in the Algerian Basin and its interaction with the large scale ocean dynamics of the Western Mediterranean Sea.

English

In attempt to study the spatial differences in autumnal equatorial upwelling intensity relative to bio-productivity in the eastern equatorial Atlantic, oceanographic in situ data along regions 10&deg;W, 0&deg;E, 2.5&deg;E and 6&deg;E, collected in the Gulf of Guinea during autumn cruise carried out in September 2007 were analyzed. The surface mean values for temperature along 10&deg;W, 0&deg;E, 2.5&deg;E and 6&deg;E are 25.02, 26.15, 26.88 and 25.60&deg;C, respectively. There was eastward weakening of the equatorial undercurrent from 10&deg;W until its complete disappearance at 6&deg;E. The highest concentration of nitrate recorded at the surface at 10&deg;W was attributed to the shoaling pycnocline observed at this region. The surface mean values for nitrate along 10&deg;W, 0&deg;E, 2.5&deg;E and 6&deg;E are 0.37, 0.09, 0.04 and 0.04 &mu;mol.kg-1, respectively. In response to the shoaling pycnocline at 10&deg;W, corresponding to the highest concentration of chlorophyll fluorescence was recorded at this region. The surface mean values for chlorophyll fluorescence along 10&deg;W, 0&deg;E, 2.5&deg;E and 6&deg;E are 0.34, 0.05, 0.07 and 0.08 mg/m3, respectively. Contributions to equatorial upwelling by the equatorial undercurrent were the strongest and mostly expressed along 10&deg;W. Profiles for apparent oxygen utilization and chlorophyll fluorescence gave indications that biological response to surface enrichments within the equatorial bands was highest at region 10&deg;W. Vertical sections for studied parameters were unsuggestive of westward advection from 6&deg;E to 10&deg;W within the equatorial band, and this signifies the important role of vertical processes in equatorial enrichment at 10&deg;W during boreal autumn. Key words: Vertical mixing, zonal advection, equatorial undercurrent, equatorial upwelling, Gulf of Guinea, nutrients, phytoplankton biomass, surface enrichment. &nbsp

Gaussian decomposition and component pigment spectral analysis of phytoplankton absorption spectra

The absorption spectrum of phytoplankton is an important bio-optical parameter for ocean color hyperspectral remote sensing; its magnitude and shape can be affected considerably by pigment composition and concentration. We conducted Gaussian decomposition to the absorption spectra of phytoplankton pigment and studied the spectral components of the phytoplankton, in which the package effect was investigated using pigment concentration data and phytoplankton absorption spectra. The decomposition results were compared with the corresponding concentrations of the five main pigment groups (chlorophylls a, b, and c, photo-synthetic carotenoids (PSC), and photo-protective carotenoids (PPC)). The results indicate that the majority of residual errors in the Gaussian decomposition are <0.001 m−1, and R2 of the power regression between characteristic bands and HPLC pigment concentrations (except for chlorophyll b) was 0.65 or greater for surface water samples at autumn cruise. In addition, we determined a strong predictive capability for chlorophylls a, c, PPC, and PSC. We also tested the estimation of pigment concentrations from the empirical specific absorption coefficient of pigment composition. The empirical decomposition showed that the Ficek model was the closest to the original spectra with the smallest residual errors. The pigment decomposition results and HPLC measurements of pigment concentration are in a high consistency as the scatter plots are distributed largely near the 1:1 line in spite of prominent seasonal variations. The Woźniak model showed a better fit than the Ficek model for Chl a, and the median relative error was small. The pigment component information estimated from the phytoplankton absorption spectra can help better remote sensing of hyperspectral ocean color that related to the changes in phytoplankton communities and varieties.

Neustonic zooplankton in the northeastern Persian Gulf

The Persian Gulf is an important area in terms of ecological values and fisheries resources. It also provides a supportive spawning and nursery areas for the finfish and shellfish communities, whose survival depends on the availability of the neustonic zooplankton. Neuston composition, abundance, and distribution were studied during two oceanographic cruises in autumn (Nov. to Dec.) 2012 and summer (Aug.) 2013 aboard R/V Ja Nay Band from 26 stations along the northeast Persian Gulf. Samples were collected in duplicate using a rectangular frame (300μm mesh net). Copepods (including copepodites) were the dominant constituents of the zooplankton and accounted for 56.7% and 69.2% of the total zooneuston populations during autumn and summer cruises, respectively. Among zooneuston, copepod biodiversity was relatively high with thirty-four copepod species in twenty two genera present. The other major groups of zooplankton in term of abundance were fish larvae and eggs 15.2%, urochordates 10.1%, decapods and other crustaceans 6.2%, cladocerans 3.8%, cnidarians 2.7% and chaetognaths 2.4% during the autumn cruise. In contrast, during the summer cruise, the other most abundant zooneuston were urochordates 7.5%, decapods 6.8%, cnidarians 6.1%, chaetognaths 3.8% and fish larva and eggs 1.5%. Zooneuston composition differed slightly in different cruises. Zooneuston abundance was slightly higher during autumn (mean of 295 ± 61 ind. m−3) than summer (231 ± 61 ind. m−3). Total zooneuston abundances were not significantly different (p > 0.05) in both spatial and temporal scales, but their copepod abundances were spatially significant (p < 0.05). Among marine insects, Halobates sp. was the new record for the Persian Gulf.

Species composition and distribution patterns of ichthyoplankton within and outside artificial reefs in Qingshan Bay, Qingdao, China

To assess the fish attraction and shelter effects of the artificial reefs in Qingshan Bay of Qingdao, the species composition and distribution patterns of ichthyoplankton in artificial reefs were investigated using vertical and horizontal tows in 2014 and 2015. In total, 7306 fish eggs and 52 fish larvae, belonging to 4 orders, 9 families, 11 genera and 12 species, were collected during 7 cruises in spring, summer and autumn of 2014. In 2015, 10373 eggs and 159 fish larvae, belonging to 6 orders, 11 families, 14 genera and 15 species, were collected in the same period as in 2014. Perciformes were the majority for both fish eggs and larvae collected during the two surveys, followed by Pleuronectiformes. Among fish eggs, Sillago japonica and Cynoglossus joyneri were the most dominant species. Among fish larvae, S. japonica exhibited the highest dominance but was not the dominant species. The high dominant species in both fish eggs and larvae appeared alternately in diffe-rent seasons. The Margalef richness index (R), Shannon diversity index (H) and Pielou evenness index (J) of ichthyoplankton community were low during the spring, summer, and autumn, showing an instable community structure of ichthyoplankton. The average trophic level of adult fish corresponding to the ichthyoplankton collected in the two years were 3.71 and 3.78, respectively, and both belonged to low carnivorous fish of third trophic level. All the species were either warm-tempe-rate species or warm-water species, which was coincident with the warm-temperate zone characteristic. Comprehensive analysis showed that the biodiversity of the ichthyoplankton community within the artificial reef areas was higher than that outside the artificial reef areas, which might be linked to flow velocity, flow field characteristics, or spatial heterogeneity of artificial reef areas.

GEM in the marine atmosphere and air-sea exchange of Hg during late autumn and winter cruise campaigns over the marginal seas of China

East Asia is one of the primary sources of atmospheric gaseous elemental mercury (GEM) among the world. In this study, GEM concentrations were measured during two cruises in late autumn and winter of 2012 and 2013 which passed through the marginal seas of China. The results show that the mean GEM concentration was 1.65ng/m3 from the South China Sea to the Yellow Sea during the 2012 cruise. While the mean GEM concentration was 2.38ng/m3 in the South Yellow Sea, and 1.75ng/m3 in the North Yellow and Bohai Seas during the 2013 cruise. High GEM contents were detected when the steering wind was offshore. There is a significant positive relationship between GEM and air temperature for these two cruises. Low GEM content was presented when the cold northerly monsoon prevailed while air masses mainly came from the clean northern oceanic region. Dissolved gaseous mercury (DGM) concentration in the surface water of the south Yellow and Bohai seas were 74.4±28pg/L. DGM concentrations were correlated with water temperature (r=0.244, p<0.05). Sea-air flux of mercury in the Yellow Sea and Bohai Sea were 11.3ng/(m2·h), ranging between −9.4 and 59.3ng/(m2·h) which was different from other seasons. The deposition of mercury appeared in the Bohai Sea affected by land polluted air and low wind speed. High flux values were caused by the northerly monsoon which carried remote clean air to the sea, with large wind speeds. The northerly monsoon is an important factor affecting the GEM transport offshore to marginal sea and the cycle of mercury in the sea in late autumn and winter.

Latitudinal and Seasonal Distribution of Particulate MSA over the Atlantic using a Validated Quantification Method with HR-ToF-AMS.

Methanesulfonic acid (MSA) has been widely used as a proxy for marine biogenic sources, but it is still a challenge to provide an accurate MSA mass concentration with high time resolution. This study offers an improved MSA quantification method using high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Particularly, the method was validated based on an excellent agreement with parallel offline measurements (slope = 0.88, R2 = 0.89). This comparison is much better than those using previously reported methods, resulting in underestimations of 31-54% of MSA concentration. With this new method, MSA mass concentrations were obtained during 4 North/South Atlantic cruises in spring and autumn of 2011 and 2012. The seasonal and spatial variation of the particulate MSA mass concentration as well as the MSA to non-sea-salt sulfate ratio (MSA:nssSO4) over the North/South Atlantic Ocean were determined for the first time. Seasonal variation of the MSA mass concentration was observed, with higher values in spring (0.03 μg m-3) than in autumn (0.01 μg m-3). The investigation of MSA:nssSO4 suggests a ubiquitous and significant influence of anthropogenic sources on aerosols in the marine boundary layer.

Surface ocean carbon dioxide during the Atlantic Meridional Transect (1995–2013); evidence of ocean acidification

Here we present more than 21,000 observations of carbon dioxide fugacity in air and seawater (fCO2) along the Atlantic Meridional Transect (AMT) programme for the period 1995–2013. Our dataset consists of 11 southbound and 2 northbound cruises in boreal autumn and spring respectively. Our paper is primarily focused on change in the surface-ocean carbonate system during southbound cruises. We used observed fCO2 and total alkalinity (TA), derived from salinity and temperature, to estimate dissolved inorganic carbon (DIC) and pH (total scale). Using this approach, estimated pH was consistent with spectrophotometric measurements carried out on 3 of our cruises. The AMT cruises transect a range of biogeographic provinces where surface Chlorophyll-α spans two orders of magnitude (mesotrophic high latitudes to oligotrophic subtropical gyres). We found that surface Chlorophyll-α was negatively correlated with fCO2, but that the deep chlorophyll maximum was not a controlling variable for fCO2. Our data show clear evidence of ocean acidification across 100° of latitude in the Atlantic Ocean. Over the period 1995–2013 we estimated annual rates of change in: (a) sea surface temperature of 0.01±0.05°C, (b) seawater fCO2 of 1.44±0.84μatm, (c) DIC of 0.87±1.02μmolper kg and (d) pH of −0.0013±0.0009 units. Monte Carlo simulations propagating the respective analytical uncertainties showed that the latter were < 5% of the observed trends. Seawater fCO2 increased at the same rate as atmospheric CO2.

English

Oceanographic in situ data collected in the Gulf of Guinea during six cruises carried out between 2005 and 2007 were analysed to study the influence of equatorial upwelling on the productivity of the region. At 10°W, observations during boreal summer and autumn cruises captured seasonal upwelling influences. In response to the shoaling pycnocline in June 2005, higher concentrations of nitrate and chlorophyll fluorescence were recorded at the ocean surface in June than in September. Our findings challenge the paradigm that westward advection from the nutrient-rich African coast is responsible for equatorial enrichment in the Gulf of Guinea. Vertical sections of the parameters under study in the summer of 2005 showed no westward advection from 3°E to 10°W within the equatorial band. This emphasizes the important role of vertical processes in equatorial enrichment at 10°W. An additional aspect of our study provides evidence of the impact on nutrient and chlorophyll distribution of off-equatorial westward recirculation of equatorial undercurrent waters (observed between 2°and 3°S). Key words: Advection, equatorial undercurrent, equatorial upwelling, Gulf of Guinea, nutrients, phytoplankton biomass.

Chemical Characteristics and Source Analysis of Aerosol Composition over the Bohai Sea and the Yellow Sea in Spring and Autumn

Abstract The total suspended particulate (TSP) samples over the Bohai Sea and the Yellow Sea were collected during two cruises in spring and autumn in 2012. Concentrations of water-soluble ions {Na+, K+, NH4+, Mg2+, Ca2+, Cl−, NO3 −, SO42−, and CH3SO3 − [methanesulfonic acid (MSA)]} and trace metals (Al, Pb, Zn, Cd, Cu, and V) were measured. Mass concentrations of TSP samples ranged from 65.2 to 136 μg m−3 in spring and from 15.9 to 70.3 μg m−3 in autumn, with average values of 100 ± 22.4 and 40.2 ± 17.8 μg m−3, respectively. The aerosol was acidic throughout the sampling periods according to calculation of equivalent concentrations of the cations (NH4+, nss-Ca2+, and nss-K+) and anions (nss-SO42− and NO3 −). Correlation analysis and enrichment factors revealed that the aerosol composition in the coastal marine atmosphere had a feature of a mixture of air masses: that is, crustal, marine, and anthropogenic emissions. Trace metals were enriched by a wide range of 1–103, and enrichment factors for crustal source (EFc) were relatively higher in spring. Species like Cd, Zn, and Pb had an overwhelming contribution from anthropogenic sources. In addition, the concentrations of MSA varied from 0.0075 to 0.17 and from 0.0019 to 0.018 μg m−3 during the spring and autumn cruises, respectively, with means of 0.061 and 0.012 μg m−3, respectively. Based on the observed MSA and nss-SO42− concentrations in spring and autumn, the relative biogenic sulfur contributions to nss-SO42− were estimated to be 8.0% and 3.5% on average, respectively, implying that anthropogenic sources had a dominant contribution to the sulfur budget over the observational area.

Stratocumulus-Topped Marine Boundary Layer Processes Revealed by the Absence of Profiler Reflectivity

AbstractStratocumulus (Sc) clouds occur frequently over the cold waters of the southeastern Pacific Ocean. Data collected during two Pan American Climate Study research cruises in the tropical eastern Pacific illuminate many aspects of this Sc-topped marine boundary layer (MBL). Here the focus is on understanding gaps in detectable wind-profiler reflectivities during two boreal autumn cruises. After rigorous quality control that included applying the Riddle threshold of minimum signal-to-noise ratio (SNR) detectability, there are many instances with no measurable atmospheric signals through a depth of up to several hundred meters, often lasting for an hour or more. Rain gauge data from the autumn 2004 cruise are used to calibrate the profiler, which allows SNR to be converted to both equivalent reflectivity and the structure-function parameter of the index of refraction . Profiles of statistics from the two profiler modes (resolutions) highlight the wide range of during a 24-h period and bound the atmosphere’s when low-mode gaps are not mirrored in the high-mode data. Considering the gaps in terms of allows them to be understood as indications of reduced “top down” buoyancy processes and/or reduced turbulent intensity, both of which have been demonstrated by previous researchers to be associated with decoupling within the Sc-topped MBL. A decoupling index calculated from surface and ceilometer data strongly suggests that decoupled conditions were common and that the MBL was coupled when gaps in profiler reflectivity were unlikely. Further study of data from other cruises may lead to a method of using profiler reflectivity as an indicator of decoupled conditions.

A potentially universal algorithm for estimating aerosol scattering reflectance from satellite remote sensing data

Accuracy of aerosol scattering reflectance in atmospheric correction is crucial for satellite ocean color remote sensing. A new approach is developed to estimate aerosol scattering reflectance from satellite data based on a look-up table of in situ water-leaving reflectance. A decision rule is set to determine the water-leaving component of the total satellite-measured radiance from the table under an assumption that aerosol scattering reflectance follows the Angstrom law. The epsilon spectrum, obtained from the ratio of aerosol scattering reflectance, is used to select the two closest aerosol models for determining the corrected epsilon values, which is adjusted to new values according to the reference wavelength. The actual aerosol scattering reflectance is obtained from the mean value of the reflectance and the new epsilon spectrum. The performance of the model is evaluated using the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) imagery, showing that the component of aerosol scattering reflectance can be completely separated from the total satellite-measured radiance, and effects of non-zero water-leaving reflectance can be eliminated over highly turbid waters. The accuracy is validated by in situ measured aerosol optical thickness (AOT) using a handheld multi-band sun photometer and the Aerosol Robotic Network (AERONET) measured AOT data during the 2006 winter cruise and 2007 autumn cruise over the East China Sea (ECS). The analysis gives the mean relative errors of 23.73% and 32.04%, respectively. Our analysis shows that aerosol scattering reflectance can be significantly overestimated over turbid waters when using the atmospheric correction method based on the black ocean assumption (BOA). It may also have some errors over oceanic waters because a small 1% bias of satellite-measured reflectance in the near-infrared (NIR) bands will lead to a relatively large error of ~10% in aerosol scattering reflectance in Band 1. This error will spread to water-leaving reflectance, possibly leading to negative values of water-leaving reflectance. This amplifying effect of aerosol scattering reflectance can be limited by matching aerosol models using epsilon spectrum in our model. Because the assumption of aerosol scattering reflectance following the Angstrom law can eliminate effects of different types of waters including open ocean, coastal regions, lakes and rivers, our model offers a potentially universal algorithm for estimating aerosol scattering reflectance from satellite remote sensing data.