Integrated Primary Production Research Articles

Deepening of the thermocline increases primary production in winter vs summer in the northern South China Sea

Primary production (PP) is higher in winter than in summer in the northern South China Sea (NSCS), which is different from temperate seas. Few field studies have been conducted to examine the regulatory factors of the seasonal difference in PP. In this study, we conducted two cruises to investigate PP in large areas in the NSCS in summer and winter. In summer, integrated primary production (IPP) was about 349 mg C m−2 d−1, lower than the winter value of around 449 mg C m−2 d−1. IPP exhibited no significant seasonal difference on the shelf between summer and winter, while beyond the shelf, IPP was significantly (p<0.05) higher in winter compared to summer. Deepening of the thermocline increased the availability of nutrients in the upper euphotic layer and was responsible for the increased IPP in winter. Furthermore, the deepened thermocline induced changes in the photosynthetic efficiency and light adaptation of the phytoplankton community, which might be another important reason for the IPP increase in winter. Integrated new production (INP) and POC flux exported from the euphotic layer were also higher in winter than in summer. The increase in POC flux was more pronounced compared to INP because in addition to being affected like INP by the increase in nutrient supply and IPP in winter, the decrease of sea surface temperature would also lead to an increase in POC flux.

Optimal Assimilation Number of Phytoplankton in the Siberian Seas: Spatiotemporal Variability, Environmental Control and Estimation Using a Region-Specific Model

The maximal value of the chlorophyll-specific carbon fixation rate in the water column or the optimal assimilation number (Pbopt) is an important parameter used to estimate water column integrated primary production (IPP) using models and satellite-derived data. The spatiotemporal variability in the Pbopt of the total and size-fractionated phytoplankton in the Siberian Seas (SSs) and its links with environmental factors were studied based on long-term (1993–2020) field and satellite-derived (MODIS-Aqua) observations. The average value of Pbopt in the SSs was equal to 1.38 ± 0.76 mgC (mg Chl a)–1 h–1. The monthly average values of Pbopt decreased during the growing season from 1.95 mgC (mg Chl a)–1 h–1 in July to 0.64 mgC (mg Chl a)–1 h–1 in October. The average value of Pbopt for small (&lt;3 μm) phytoplankton 1.6-fold exceeded that for large (&gt;3 μm) phytoplankton. The values of Pbopt depend mainly on incident photosynthetically available radiation (PAR). Based on the relationship between Pbopt and PAR, the empirical region-specific algorithm (E0reg) was developed. The E0reg algorithm performed better than commonly used temperature-based models. The application of E0reg for the calculation of Pbopt will make it possible to more precisely estimate IPP in the SSs.

Photosynthesis‐Irradiance Response in the Eddy Dipole in the Western South China Sea

AbstractPhotosynthesis‐irradiance (P‐E) parameters, such as the maximum photosynthetic rate () and maximum light utilization coefficient (α), are key parameters of primary production (PP) models. It is necessary to understand the response of P‐E parameters to mesoscale eddies to accurately model PP in eddies. The P‐E parameters and phytoplankton communities were examined at the surface and the deep chlorophyll maximum (DCM) of the eddy dipole in the western South China Sea. The surface differed significantly between the edge and center of both eddies. The at the center was significantly higher than that at the edge of the cyclonic eddy (CE), while the opposite trend was observed in the anticyclonic eddy (AE). Phytoplankton community composition modulated variability in P‐E parameters in the eddy dipole. Over 75% of the variance in surface P‐E parameters could be explained by the pico‐phytoplankton communities and environmental factors (nutrients and temperature). In contrast, the ratio of Synechococcus abundance to chlorophyll a concentration was primarily responsible for the variability in P‐E parameters at the DCM. These relationships allowed us to model and α at all stations and depths sampled. The integrated primary production (IPP) determined from these modeled P‐E parameters was coincident with the IPP determined from on‐deck incubations. The modeled ‐α‐based IPP exhibited a higher IPP at the CE center than that at the AE center. Our findings can improve the parameterization of the physical‐biogeochemical coupling models of eddies.

Vertical Variability of Primary Production and Features of the Subsurface Chlorophyll Maximum in the Laptev Sea in August–September, 2015, 2017, and 2018

The vertical distribution of phytoplankton primary production (PP) and chlorophyll a (Chl) was studied based on the data carried out in August–September 2015, 2017, and 2018. The PP maximum was located at the surface or within the 0–5 m subsurface layer. The subsurface chlorophyll maximum (SCM) was recorded at 39% stations on the outer shelf and in the vicinity of the continental slope. The SCM was not detected along the northward transect (130° E) from the Lena River delta. As in other areas of the World Ocean, the SCM was located below the upper mixed layer (UML), in the nitracline, near the boundary of the euphotic zone (1% of photosynthetically active radiation). Generally, the SCM was not accompanied by an additional PP maximum. The Chl concentration at the SCM did not exceed 1 mg m–3. PP produced within the UML and SCM contributed 72 and 23%, respectively, to the integrated primary production (IPP) of the water column. Our results suggest that the influence of the SCM on IPP was insufficient due to low Chl concentration and PP colimitation by the low light and temperature at these depths.

Seasonal Variations of Marine Environment and Primary Production in the Taiwan Strait

The first data set of seasonal marine environment and euphotic zone integrated primary production (IP) variations in the Taiwan Strait was reported. The measured annual IP was 123±86 gC m-2 y-1 (338±235 mgC m-2 d-1), and its seasonal variations can be described with a left-skewed normal distribution curve. The average seasonal IP values from the highest to the lowest were summer (664±270 mgC m-2 d-1), autumn (350±118 mgC m-2 d-1), spring (202±110 mgC m-2 d-1) and winter (137±68 mgC m-2 d-1). The lowest IP was during the nutrient-rich winter because it had a short insolation duration, low incident photosynthetic active radiation (PAR) and low light transmission (shallow euphotic zone depth) due to strong vertical mixing. In contrast to the winter, the highest IP was during the nutrient-depleted summer, which had a long insolation duration, high incident PAR and high light transmission (deeper euphotic zone depth). In addition, the heterotrophic nutrients from upwelling in the south might also support the highest IP in summer. As three primary water masses exist in the Taiwan Strait and three of them have different characteristics, different mixing ratios of water masses may cause different chemical and hydrographic conditions, which leads to different levels of Chl a concentrations and primary production. It is worth to mention that offshore wind farm (OWF) construction in the Changyun Rise (CYR) of the Taiwan Strait is on-going. As primary production is the foundation for a marine ecosystem and supports the food web and fish stock, the results of this research can not only be used as the baseline for evaluating the OWF impact on the marine ecosystem but also be used for assessing their influence on fishery resources.

Spatial variability of phytoplankton primary production characteristics in the North Atlantic in summer 2013

Spatial variability of phytoplankton primary production characteristics has been studied along the transects between Shetland Islands and Iceland (transect I) and along 59.5° N (transect II) from 30 June to 16 July 2013. It has been shown that surface chlorophyll a concentration (Chl0) varied more than two order of magnitude from 0.07 to 6.67 mg/m3 (transect I) and from 0.02 to 3.63 mg/m3 (transect II). Water column integrated primary production (IPP) changed by a factor of 3.8 from 273 to 1040 and by a factor of 5.6 from 68 to 379 mgC/m2 per day along transects I and II, respectively. It has been established that spatial variability of Chl0 and IPP was consistent with distribution of the main surface flows and thermohaline fronts. That conclusion was made on the basis of reliable positive correlation between Chl0 and the zonal potential temperature gradient (R = 0.43, p &lt; 0.01, N = 65). Phytoplankton assimilation activity along transect II depends on nutrients concentration. That conclusion was confirmed by reliable positive correlation between optimum chlorophyll specific carbon fixation rate (Pbopt) and phosphate concentration (R = 0.58, p &lt; 0.05, N = 76) and between Pbopt and dissolved silica (R = 0.51, p &lt; 0.05, N = 76).

Spatial and vertical variability of primary production in the Kara Sea in July and August 2016: the influence of the river plume and subsurface chlorophyll maxima

Seasonal variations in primary production (PP) in the Kara Sea are underresearched. Previous studies only collected data during autumn or in late summer. However, the middle of summer is close to the beginning of the growing season, when PP can contribute significantly to annual water column integrated primary production (IPP). In addition, differences can be expected in the spatial and vertical distribution of phytoplankton communities in this period. This gap in midsummer data was addressed within the framework of a multidisciplinary research cruise by the R/V “Akademik Mstislav Keldysh” (from 15 July to 18 August 2016). High values of IPP (> 200 mgC m−2 day−1) and surface chlorophyll a (Chl a) concentration (Chl0 > 1 mg m−3) were associated with the Ob–Yenisey river plume, located in the central part of the Kara Sea. Beyond the influence of the plume, in the western and southwestern regions of the Kara Sea, well-pronounced subsurface chlorophyll maxima (SCM) were observed. In some cases, the Chl a concentration in SCM exceeded Chl0 by two orders of magnitude. SCM were often accompanied by subsurface PP maxima (SPM). At stations where SCM was pronounced, IPP values reached 500–800 mgC m−2 day−1, and > 30 % of IPP was accounted for by SPM-integrated PP. Thus, in the middle of summer in the Kara Sea, IPP was linked with the chlorophyll-specific phytoplankton biomass and depended on the strength of the SCM.

Modelling Kara Sea phytoplankton primary production: Development and skill assessment of regional algorithms

Empirical region-specific (RSM), depth-integrated (DIM) and depth-resolved (DRM) primary production models are developed based on data from the Kara Sea during the autumn (September–October 1993, 2007, 2011). The model is validated by using field and satellite (MODIS-Aqua) observations. Our findings suggest that RSM algorithms perform better than non-region-specific algorithms (NRSM) in terms of regression analysis, root-mean-square difference (RMSD) and model efficiency. In general, the RSM and NRSM underestimate or overestimate the in situ water column integrated primary production (IPP) by a factor of 2 and 2.8, respectively. Additionally, our results suggest that the model skill of the RSM increases when the chlorophyll specific carbon fixation rate, efficiency of photosynthesis and photosynthetically available radiation (PAR) are used as input variables. The parameterization of chlorophyll (chl a) vertical profiles is performed in Kara Sea waters with different trophic statuses. Model validation with field data suggests that the DIM and DRM algorithms perform equally (RMSD of 0.29 and 0.31, respectively). No changes in the performance of the DIM and DRM algorithms are observed (RMSD of 0.30 and 0.31, respectively) when satellite-derived chl a, PAR and the diffuse attenuation coefficient (Kd) are applied as input variables.

Linking phytoplankton nitrogen uptake, macronutrients and chlorophyll- a in SW Atlantic waters: The case of the Gulf of San Jorge, Argentina

Abstract We compared biological and chemical parameters in surface waters of the Gulf of San Jorge to better understand carbon export and the factors that control phytoplankton production in an area of the Argentinian Continental Shelf, a vastly under sampled region of the SW Atlantic Ocean. In April of 2012, we estimated new and regenerated primary production in the Gulf by measuring nitrate and ammonium uptake, respectively. We also measured macronutrient, and in situ chlorophyll- a concentrations, which were compared to chlorophyll- a estimates from remote sensing. Although the Gulf of San Jorge presents high levels of chlorophyll- a and primary production, the relationship between these parameters is not straightforward. Previous studies showed that surface chlorophyll- a explains only part of the variance in euphotic-zone integrated primary production, and that satellite-derived chlorophyll- a underestimates in situ primary production. Our results showed large spatial variability in the Gulf, with transitional physico-chemical conditions, such as fronts, that could favor an increase in biological production. In situ chlorophyll- a concentrations were highest at the mid-shelf station (6.0 mg m − 3 ) and lowest at the northernmost location by an order of magnitude. Remote sensing measurements of chlorophyll- a underestimated our in situ chlorophyll- a concentrations. Total nitrogen (nitrate + ammonium) uptake showed relatively similar rates throughout the study area (≈ 130 nM-N d − 1 ), except in the northernmost station where it was much lower (53 nM-N d − 1 ). This north region had a distinct water mass and maximal levels of macronutrients (nitrate ≈ 6 μM, ammonium ≈ 1.2 μM, phosphate ≈ 1.2 μM and silicic acid ≈ 4 μM). For the entire sampling region, chlorophyll- a concentrations strongly correlated with total nitrogen uptake (r = 0.76, n = 8, p 2 balance.

Decadal trends in phytoplankton production in the Pacific Arctic Region from 1950 to 2012

This paper provides a synthesis of available in situ primary production (PP) measurements from the Pacific Arctic Region (PAR), collected between 1950 and 2012. Seasonal integrated primary production (IPP) across the PAR was calculated from 524 profiles, 340 of which were also analyzed to determine the average vertical distribution of PP rates for spring, summer and fall months. The Chirikov Basin and Chukchi Shelf were the most productive areas, with the East Siberian Sea, Chukchi Plateau and Canada Basin the lowest. Decadal-scale changes were indicated in the southern Chukchi Sea, and across Hanna Shoal. In the southern Chukchi Sea in August, IPP increased significantly from 113±35mgCm-2 d-1 in 1959 and 1960 to 833±307mgCm-2 d-1 in the 2000s. Increases in the magnitude of IPP were accompanied by variations in the vertical distribution, the subsurface peak observed in the 1959/60 was not present in the 2000s. The mechanism behind this change was undetermined but could have included changes in stratification, mixing or surface distribution of water masses as well as methodological differences. Over Hanna Shoal, the phytoplankton surface bloom now occurs earlier by several weeks compared to 1993, linked to increases in light due to earlier sea- ice retreat. In 1993 with sea ice still present in the region the surface bloom occurred in August, in 2002 and 2004 this same period was characterized by open water and low surface PP and strong subsurface production. This dataset provides a region-wide quantification of IPP and decadal trends and highlights the need for a cooperative monitoring program to observe the long-term impacts of climate change in the Arctic ecosystem.

Seasonal variation of the satellite-derived phytoplankton primary production in the Kara Sea

Seasonal variation of the integrated primary production (IPP) and surface chlorophyll (Chl0) in different regions of the Kara Sea was studied from satellite data obtained by the MODIS-Aqua colour scanner and averaged for 2003–2015. The minimum variation of Chl0 concentration during the growing season (from April to October) was 1.5 times in southwestern region and 2 times in the northern region of the sea. It was found that the Chl0 concentration increased slightly in all regions by the end of the growing season. The maximum IPP value recorded in June coincided with the peak level of photosynthetically active radiation (PAR) and maximum river discharge. The IPP value varied in a wider range compared with the Chl0 concentration. The ratio of the maximum and minimum monthly average IPP values varied from 8.9 times in Southwestern region to 11.7 times in the Northern region of the sea. The average increase in the Chl0 concentration was 1.7 times (from 0.78 mg/m3 in April to 1.29 mg/m3 in October). The IPP value varied by a factor of 10.7 (from 26 mg C/m2 per day in October to 279 mg C/m2 per day in June). The article also discusses the influence of water column stratification, the concentration of nutrients, the PAR level, and river discharge on the seasonal IPP dynamics in the Kara Sea.

Contributions of physical and biogeochemical processes to phytoplankton biomass enhancement in the surface and subsurface layers during the passage of Typhoon Damrey

AbstractIn this study, a one‐dimensional physical‐biogeochemical coupled model was established to investigate the responses of the upper ocean to Typhoon Damrey in the basin area of the South China Sea. The surface chlorophyll a concentration (Chl a) increased rapidly from 0.07 to 0.17 mg m−3 when the typhoon arrived and then gradually reached a peak of 0.61 mg m−3 after the typhoon's passage. The subsurface Chl a decreased from 0.34 to 0.17 mg m−3 as the typhoon arrived and then increased gradually to 0.71 mg m−3. Analyses of model results indicated that the initial rapid increase in the surface Chl a and the decrease in the subsurface Chl a were caused mainly by physical process (vertical mixing), whereas the subsequent gradual increases in the Chl a in both the surface and subsurface layers were due mainly to biogeochemical processes (net growth of phytoplankton). The gradual increase in the Chl a lasted for longer in the subsurface layer than in the surface layer. Typhoon Damrey yielded an integrated primary production (IPP) of 6.5 × 103 mg C m−2 (~14% of the annual IPP in this region).

Verification of Kara Sea primary production models with field and satellite observations

The depth-integrated model (Ψ-Mod) and depth-resolved Kara Sea model (KDRSM) of primary production in the water column were verified using field (2013–2015) and satellite (MODIS-Aqua scanner, 2007, 2011, 2013–2015) observations. The KSDRM and Ψ-Mod over- or underestimate the values of integrated primary production (IPP) in autumn by a factor of 2 and 2.5 with shipboard data as input parameters; the rootmean-square difference (RMSD) was 0.29 and 0.39, respectively. In summer, the efficiency of Ψ-Mod decreased by a factor of 1.5 (RMSD = 0.57), while the predictive capacity of the KSDRM remained the same (RMSD = 0.31). In the Laptev Sea in autumn, the KSDRM performed better than Ψ-Mod (the RMSD was 0.24 and 0.41, respectively). There was no sufficient decrease in the predictive skill of either algorithm when MODIS-Aqua data were used as input parameters. Thus, Ψ-Mod, being a simple and precise algorithm, can be recommended for evaluating the annual IPP in the Kara Sea and for studying its long-term variability using satellite data.

Impact on primary production by mesoscale eddies in the northwest South China Sea: A case study by satellite and field observation

Phytoplankton biomass and production coupled with environmental parameters were investigated in northwestern South China Sea during the South China Sea Open Cruise by R/V “Shiyan 3” in September 2009. Both satellite and in situ data indicated that cold eddy decreased sea surface temperature and enhanced Primary production (PP) around Xisha Island adjacent sea. Nutricline, thermocline and chlorophyll a contour line were coincident generally in the eastern part of the Y area, indicating the impact of hydrological processes on ecological and environmental profiles. PP decreased with the increasing water depth in the euphotic layer, and the maximum value appeared in the surface layer. The surface PP value was 0.59 mgC m−3 h−1 and the integrated primary production (IPP) was 250 mgC m−2 d−1 at Y2, slightly lower than that at X5, with the surface PP value of 0.66 mgC m−3 h−1 and the IPP value of 259.33 mgC m−2 d−1. The descend range of IPP in Y area was higher than the ascensional range in X area, indicating that the impact of cold eddy on phytoplankton biomass and production was more obvious than the impact of the warm eddy in this study.

Lake-wide phytoplankton production and abundance in the Upper Great Lakes: 2010–2013

Lake-wide phytoplankton chlorophyll a concentrations and primary production were determined for lakes Huron, Michigan, and Superior in 2010–2013. Chlorophyll a concentrations were determined using MODIS imagery with a color-producing agent algorithm and primary production with the Great Lakes Production Model using remotely sensed and empirically derived input from the Upper Great Lakes. The new chlorophyll a and primary production estimates agreed well with field measurements. Lake-wide mean chlorophyll a concentrations determined from observations in all 12 months were highest in Lake Superior (mean = 0.99 mg/m3), intermediate in Lake Michigan (mean = 0.88 mg/m3), and lowest in Lake Huron (mean = 0.77 mg/m3). In Lake Superior, a gradient in chlorophyll a concentrations was noted from the shallow zone (0–30 m, mean = 1.57 mg/m3) to the deep-water zone (> 150 m, mean = 0.94 mg/m3). However, in Lake Michigan, no differences in mean chlorophyll a concentrations were noted in shallow-, mid-, or deep-water zones (means, 0.83, 0.86, 0.90 mg/m3, respectively). Lake-wide areal integrated primary production rates in lakes Huron, Michigan, and Superior were not significantly different for the 2010–2013 period (means, 216, 259, and 228 mg C/m2/d, respectively). Also, primary production in all depth zones (shallow, mid, and deep) were similar across lakes. Annual whole-lake phytoplankton carbon fixation values for 2010–2013 ranged from 4.4 to 5.7 Tg/y for Lake Huron, 5.0–7.2 Tg/y for Lake Michigan, and 6.4–9.5 Tg/y for Lake Superior.

Influence of mesoscale eddies on primary production in the South China Sea during spring inter-monsoon period

Mesoscale eddies have been suggested to have an impact on biological carbon fixation in the South China Sea (SCS). However, their overall contribution to primary production during the spring inter-monsoon period is still unknown. Based on large-scale biological and environmental in situ observations and synchronous remote sensing data, the distribution patterns of phytoplankton biomass and the primary production, and the role of mesoscale eddies in regulating primary production in different eddy-controlled waters were investigated. The results suggested that the surface chlorophyll a concentrations and water column integrated primary production (IPP) are significantly higher in cyclonic eddies and lower in the anticyclonic eddies as compared to that in non-eddy waters. Although eddies could affect various environmental factors, such as nutrients, temperature and light availability, nutrient supply is suggested to be the most important one through which mesoscale eddies regulated the distribution patterns of phytoplankton biomass and primary production. The estimated IPP in cyclonic and anticyclonic eddies are about 29.5% higher and 16.6% lower than the total average in the whole study area, respectively, indicating that the promotion effect of mesoscale cold eddies on the primary production was much stronger than the inhibition effect of the warm eddies per unit area. Overall, mesoscale eddies are crucial physical processes that affect the biological carbon fixation and the distribution pattern of primary production in the SCS open sea, especially during the spring inter-monsoon period.

Influence of anticyclonic eddies on the Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean (BOUM cruise)

Abstract. We studied a longitudinal transect in the Mediterranean Sea (MS) and along this transect, the influence of anticyclonic eddies at three long duration (LD) stations. The deep chlorophyll maximum depth, the euphotic layer depth and the top of the nitracline depth are clearly correlated outside of the eddies, and deepen from the oligotrophic western to the ultraoligotrophic eastern MS. We provide evidence that the locations of the three LD stations studied were near the axis of the eddies. Their diameters were close to 100 km and the studied areas were less than 10 km from the centre of the eddies. The positions of the LD stations are marked by an increase in the flux function and a decrease in apparent oxygen utilization (AOU) and in excess density σ), as expected for anticyclonic eddies. Integrated mean primary production measured in situ inside the three studied eddies confirms the previous conclusion that integrated primary production (IPP) about 150 mgC m−2 d−1 may appear as a lower limit for IPP during strong oligotrophic conditions. The mesoscale activity is strong enough to locally modify the very well-documented western-to-eastern gradient of trophic conditions in the MS. We proposed a new calculation for mixed layer depths (MLDs) enabling the determination of MLD to take into consideration processes occurring with time scales ranging from a few hours to several days, and also the winter MLD. Studying the main physical, chemical and dynamical characteristics of the three eddies enables us to consider that the vorticity barrier prevents any strong mixing and advection of outer water inside the eddy and explains why the depth range of eddies starts from the surface. As a first approximation, the anticyclonic eddies could be considered as closed systems dating back to the previous winter, making possible to draw first-order budgets. The daily new N-input in the photic zone is virtually identical to the N-export measured at 230 m by drifting traps. This means that the eddies are close to an equilibrium state where input is equal to loss. The annual N-input by winter convection, which is a fundamental criterion for new nutrient availability, may be extremely variable inside eddies, with W-MLD varying from 90.5 m at the western station to 396.5 m at the eastern station. W-MLDs are always deeper inside the eddies than outside where they are in keeping with climatological averages. AOU was low inside the eddies; this together with the near-identical export measured at 230 and 460 m seems to indicate that eddy cores are areas where low mineralisation of particulate organic matter occurs. "In" and "out" AOU comparisons indicate lower mineralisation inside the eddies suggesting a higher efficiency for CO2 sequestration via sedimentation of particulate organic matter. The three eddies are enriched in dissolved organic carbon (DOC). Sequestration of CO2 by vertical export of accumulated DOC therefore seems to be higher inside eddies. The relative importance of DOC transport in the biological pump is probably one of the main characteristics of low-P low chlorophyll (LPLC) areas, and it is likely to be reinforced inside anticyclonic eddies. The numerous anticyclonic eddies in the MS are likely to influence the water masses and their dispersion, and therefore have a strong impact on the biogeochemical properties at the scale of the MS.

Influence of seasonal monsoons on net community production and CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in subtropical Hong Kong coastal waters

Abstract. Data from seven cruises in three different environments including the Pearl River estuary, sewage discharge outfall, and eastern coastal/shelf waters were used to examine the seasonal variations in net community production (NCP) and the biologically active gases O2 and CO2. In the winter dry season, when monsoon-induced downwelling was dominant, NCP was negative (−84 ± 50 mmol C m−2 d−1) in all three regions. The negative NCP corresponded to O2 influxes of 100 ± 50 mmol O2 m−2 d−1 and CO2 effluxes of 24 ± 10 mmol C m−2 d−1. In the summer wet season, when upwelling brought the deep oceanic waters to the coast due to the southwest monsoonal winds, there was a 2 to 15-fold increase in integrated primary production (IPP) compared to winter. The increase in IPP was likely due to the favorable conditions such as stratification and the nutrient inputs from upwelled waters and the Pearl River estuary. NCP in the mixed layer reached up to 110 ± 48 mmol C m−2 d−1 in the wet season. However, accompanying the high positive NCP, we observed an O2 influx of 100 ± 60 mmol O2 m−2 d−1 and CO2 efflux of 21 ± 15 mmol C m−2 d−1. The contradictory observation of positive NCP and CO2 release and O2 uptake in the mixed layer could be explained by the influence of the southwest monsoon-induced upwelling along with the influence of the Pearl River, as the upwelling brought cold, low dissolved oxygen (DO, 160 ± 30 μM) and high dissolved inorganic carbon (DIC, 1960 ± 100 μatm) water to the surface in the wet season. Hence, the subtropical Hong Kong coastal waters are generally a CO2 source due to the monsoonal influence during both the dry-heterotrophic and wet-autotrophic seasons.

Estimates of primary production by remote sensing in the Arctic Ocean: Assessment of accuracy with passive and active sensors

The Arctic Ocean, including its regional shelf seas, is assumed to play an important role in the global carbon cycle. However, the true magnitude of annual production is unknown, as in situ data are sparse in time and space. Remote sensing technology has the potential to provide large scale estimates of phytoplankton biomass at much higher frequency and spatial coverage than shipboard observations in this remote region. Subsurface peaks in both biomass and primary production (PP), which are the characteristics of the Arctic, are shown to limit the reliability of ocean color based integrated PP (IPP) models in the Chukchi Sea. Here we report that the retrievals of IPP from remotely sensed ocean color data were accurate only when limited to 1.2 optical depths, which severely constrains the utility of ocean color remote sensing for the assessment of Arctic Ocean dynamics. Active sensors such as LIDAR, can, in combination with passive ocean color, dramatically improve our ability to estimate IPP for the Arctic. IPP retrievals were improved to within a factor of 2–3 of the measured values, when the vertical distribution of Chl a was determined to a resolution of 1 m using modeled LIDAR retrievals of the beam attenuation coefficient. This was far better than models using only passive ocean color. The instrument specifications of the current NASA spaceborne LIDAR (CALIOP) allow for the retrieval of K d at a depth resolution of 23 m. Even with this constraint, however, the accuracy of the modeled IPP was improved over passive ocean color retrievals to approximately a factor of 3. The Arctic is a perfect location to merge ocean color and LIDAR measurements as the polar orbit of CALIOP provides complete grid coverage of the area every 8 days, crossing the horizontal gradients in Chl a already known to exist from passive ocean color observations.

Influence of the geostrophic transport of phosphates on primary production off Baja California (Mexico)

We estimated the net flux of inorganic phosphorus (kg P d–1) due to geostrophic transport in the upper 100 m of a control volume (CV) off Baja California (Mexico) during 2003 and 2004. The influence of this flux on integrated primary production (IPP) in the photic zone (less than 100 m depth) was estimated comparing the net P flux into the CV against the P requirements for IPP. The greatest P fluxes occurred during spring and summer 2004; the northern side of the CV was the main recipient of P. The most persistent P outflow occurred along the southern side of the CV, except in winter 2003, when there was an input of P fluxes related to cyclonic and anticyclonic eddies off Ensenada. The net geostrophic transport during 2003 and 2004 contributed enough P to support the IPP requirements during winter and spring, indicating that P was not limiting for phytoplankton organic carbon production during these seasons.