Regional Primary Productivity Research Articles

Nutrient‐Rich Winter Water Formation on the Beaufort Shelf, Arctic Ocean

AbstractNewly ventilated winter water (NVWW) is a cold, salty, nutrient‐rich water mass that is critical for supporting the ecosystem of the western Arctic Ocean and for ventilating the halocline in the Canada Basin. While the formation of NVWW is well‐documented on the Chukchi shelf, there remain fundamental questions regarding its formation on the western Beaufort shelf. In this study, we use hydrographic data from two late‐fall cruises in 2018 and 2022 to investigate the roles of sea ice production and wind‐driven upwelling in the formation of NVWW and the implications for the nutrient content of the water. For each of the shipboard transects, we apply proxies for the extent of the winter water formation and the strength of the associated upwelling, respectively. It is demonstrated that the NVWW attains higher levels of nitrate due to two factors: (a) more active formation of the water associated with enhanced sea ice production and (b) more extensive upwelling of water high in nutrients from the basin to the shelf following an easterly wind event. The latter process would be less common on the wide Chukchi shelf. These findings have significant implications for the regional primary production.

A comparative study on the spatio-temporal patterns and drivers of net primary productivity in three basins across different climate gradients in China

The comparative study on terrestrial net primary productivity in regions across climate gradients may help to better understand ecosystem response to climate change, yet is relatively understudied. Therefore, in this study, we compared the spatio-temporal patterns of net primary productivity during 2010-2019 and identify the different controls in three basins with typical climates in China: the Heihe River Basin with arid and semi-arid climate, Weihe River Basin with semi-arid and semi-humid climate, and Lower Yangtze River Basin with humid climate. Results indicated that the net primary productivity followed the order: Lower Yangtze River Basin (480.3 g C m−2 yr−1) > Weihe River Basin (346.7 g C m−2 yr−1) > Heihe River Basin (98.1 g C m−2 yr−1). The vegetation in the Heihe River Basin had severel hydrothermal limitation as the greatest importance of temperature and precipitation to the net primary productivity. In contrast, land cover type instead of climate became the most important variable on net primary productivity in the Weihe River Basin, and topography and land cover type were critical controls in the Lower Yangtze River Basin. In addition, the annual net primary productivity in all three areas exhibited an increasing trend during 2010-2019. However, the increase of net primary productivity in the Heihe River Basin was primarily driven by the increase of both temperature and precipitation due to the warming and humification in the northwestern of China. In contrast, the increase of temperature (especially spring warming) dominated the increase of net primary productivity in the Weihe River Basin and Lower Yangtze River Basin, due to the relatively sufficient precipitation. Furthermore, monthly net primary productivity exhibited a unimodal curve throughout the year. However, the increasing trend nearly stopped in June and July in the Lower Yangtze River Basin. This is possibly due to the light deficiency with abundant precipitation for plant photosynthesis in the natural ecosystem like forest and shrubland, and the rotation from wheat harvesting to rice planting in the cropland in these months.

A Radiation-Regulated Dynamic Maximum Light Use Efficiency for Improving Gross Primary Productivity Estimation

The light use efficiency (LUE) model has been widely used in regional and global terrestrial gross primary productivity (GPP) estimation due to its simple structure, few input parameters, and particular theoretical basis. As a key input parameter of the LUE model, the maximum LUE (Ɛmax) is crucial for the accurate estimation of GPP and to the interpretability of the LUE model. Currently, most studies have assumed Ɛmax as a universal constant or constants depending on vegetation type, which means that the spatiotemporal dynamics of Ɛmax were ignored, leading to obvious uncertainties in LUE-based GPP estimation. Using quality-screened daily data from the FLUXNET 2015 dataset, this paper proposed a photosynthetically active radiation (PAR)-regulated dynamic Ɛmax (PAR-Ɛmax, corresponding model named PAR-LUE) by considering the nonlinear response of vegetation photosynthesis to solar radiation. The PAR-LUE was compared with static Ɛmax-based (MODIS and EC-LUE) and spatial dynamics Ɛmax-based (D-VPM) models at 171 flux sites. Validation results showed that (1) R2 and RMSE between PAR-LUE GPP and observed GPP were 0.65 (0.44) and 2.55 (1.82) g C m−2 MJ−1 d−1 at the 8-day (annual) scale, respectively; (2) GPP estimation accuracy of PAR-LUE was higher than that of other LUE-based models (MODIS, EC-LUE, and D-VPM), specifically, R2 increased by 29.41%, 2.33%, and 12.82%, and RMSE decreased by 0.36, 0.14, and 0.34 g C m−2 MJ−1 d−1 at the annual scale; and (3) specifically, compared to the static Ɛmax-based model (MODIS and EC-LUE), PAR-LUE effectively relieved the underestimation of high GPP. Overall, the newly developed PAR-Ɛmax provided an estimation method utilizing a spatiotemporal dynamic Ɛmax, which effectively reduced the uncertainty of GPP estimation and provided a new option for the optimization of Ɛmax in the LUE model.

The Importance of Subsurface Productivity in the Pacific Arctic Gateway as Revealed by High‐Resolution Biogeochemical Surveys

AbstractFollowing sea‐ice retreat, surface waters of Arctic marginal seas become nutrient‐limited and subsurface chlorophyll maxima (SCM) develop below the pycnocline where nutrients and light conditions are favorable. However, the importance of these “hidden” features for regional productivity is not well constrained. Here, we use a unique combination of high‐resolution biogeochemical and physical observations collected on the Chukchi shelf in 2017 to constrain the fine‐scale structure of nutrients, O2, particles, SCM, and turbulence. We find large O2 excess at middepth, identified by positive saturation () maxima of 15%–20% that unambiguously indicate significant production occurring in middepth waters. The maxima coincided with a complete depletion of dissolved inorganic nitrogen (DIN = NO3− + NO2− + NH4+). Nitracline depths aligned with SCM depths and the lowest extent of maxima, suggesting this horizon represents a compensation point for balanced growth and loss. Furthermore, SCM were also associated with turbulence minima and sat just above a high turbidity bottom layer where light attenuation increased significantly. Spatially, the largest maxima were associated with high nutrient winter‐origin water masses (14.8% ± 2.4%), under a shallower pycnocline associated with seasonal melt while lower values were associated with summer‐origin water masses (7.4% ± 3.9%). Integrated O2 excesses of 800–1,200 mmol m−2 in regions overlying winter water are consistent with primary production rates that are 12%–40% of previously reported regional primary production. These data implicate short‐term and long‐term control of SCM and associated productivity by stratification, turbulence, light, and seasonal water mass formation, with corresponding potential for climate‐related sensitivities.

Vegetation restoration dominated the variation of water use efficiency in China

Implementation of numerous ecological restoration programs over the last two decades has significantly increased vegetation coverage in China. However, the response of the coupled carbon and water cycles to the large-scale vegetation restoration and the underlying mechanisms remain unclear. This study analyzed the spatiotemporal patterns of regional gross primary productivity (GPP), evapotranspiration (ET) and water use efficiency (WUE) in China using the two-leaf light use efficiency (TL-LUE) and the Priestley Taylor Jet Propulsion Laboratory (PT-JPL) models during the 2000–2017 period. The influencing mechanisms of anthropogenic re-vegetation and climatic factors on regional WUE were also analyzed. Results indicate that (1) both the GPP and WUE showed a significant increasing tendency with inter-annual change rates of 10.53 g C m−2 yr−1 and 0.01 g C kg−1 H2O yr−1, respectively; while the inter-annual change rate of annual ET was 1.43 kg H2O m−2 yr−1. (2) Spatially, the regional GPP dominated WUE variation of more than 79.51% of the total area. (3) Among the influencing factors, the greening of vegetation driven by human activities (LAIh) explained 35.27% of the WUE variation in China, much more than the climatic factors over during the study period. At the regional scale, human-driven vegetation greening also dominated the increasing WUE at regional scale. These findings provide important information to support large-scale ecological restoration policy/decision making to improve ecosystem services in China.

Primary productivity measurements in the Ross Sea, Antarctica: a regional synthesis

Abstract. Polar systems are undersampled due to the difficulty of sampling remote and challenging environments; however, these systems are critical components of global biogeochemical cycles. Measurements on primary productivity in specific areas can quantify the input of organic matter to food webs and so are of critical ecological importance as well. However, long-term measurements using the same methodology are available only for a few polar systems. Primary productivity measurements using 14C-uptake incubations from the Ross Sea, Antarctica, are synthesized, along with chlorophyll concentrations at the same depths and locations. A total of 19 independent cruises were completed and 449 stations occupied where measurements of primary productivity (each with seven depths) were completed. The incubations used the same basic simulated in situ methodology for all. Integrated water column productivity for all stations averaged 1.10 ± 1.20 g C m−2 d−1, and the maximum was 13.1 g C m−2 d−1. Annual productivity calculated from the means throughout the growing season equalled 146 g C m−2 yr−1. The mean chlorophyll concentration in the euphotic zone (the 1 % irradiance level) was 2.85 ± 2.68 mg m−3 (maximum observed concentration was 19.1 mg m−3). Maximum photosynthetic rates above the 30 % isolume (normalized to chlorophyll) averaged 0.98 ± 0.71 mg C (mg chl)−1 h−1, similar to the maximum rate found in photosynthesis–irradiance measurements. Productivity measurements are consistent with the temporal patterns of biomass found previously, with biomass and productivity peaking in late December; mixed layers were at a minimum at this time as well. Estimates of plankton composition also suggest that pre-January productivity was largely driven by the haptophyte Phaeocystis antarctica and summer productivity by diatoms. The data set (https://doi.org/10.26008/1912/bco-dmo.863815.2, Smith, 2021) will be useful for a comparison to other Antarctic regions and provide a basis for refined bio-optical models of regional primary productivity and biogeochemical models for the Southern Ocean.

Relative yield of food and efficiency of land-use in organic agriculture - A regional study

CONTEXTMost information on relative yield of organic (OA) and conventional agriculture (CA) is from plot experiments of individual crops grown with organic or inorganic fertilizers, respectively. Commonly reported values are 0.75–0.91, a relatively small difference. But organic manures are produced through biological nitrogen fixation (BNF) by legumes. How much and what else does that land in legumes contribute to overall yield? OBJECTIVEEstablishment of OA/CA yield ratios for crop-dairy production at regional scale accounting for proportions of land in crop and fodder production and their contributions to overall food yield using human metabolizable energy (HME) as a unifying parameter of yield of grain and milk. METHODSAverage yield of grain and fodder crops per unit farm area for OA and CA in eight regions of Sweden were converted to human (HME) and ruminant metabolizable energy (RME), respectively. Two diets for dairy cattle were constructed to maximize either yield of HME in grain plus milk (maxHME) or in milk (maxmilk) from all grown fodder supplemented by crop products while maintaining overall diet quality at 15% crude protein (CP). RESULTS AND CONCLUSIONSAverage regional annual primary production (dry biomass), including crop residues, of 6361 (range 4862–7793) kg/ha for OA was less than 9223 (range 6337–12,910) kg/ha in CA. OA had greater proportion of land in fodder crops and pasture (65%, range 38–87%) than CA (30%, range 11–86%). Total HME yields (grain plus milk) were less in OA than CA but with large variation between regions, maxHME OA 21.2 (range 11.0–30.4) GJ/ha and CA 43.6 (16.2–82.1) GJ/ha and maxmilk OA 19.9 (range 9.1–27.4) GJ/ha and CA 42.9 (range 16.0–80.9) GJ/ha. Regional OA/CA HME-yield ratios ranged from 0.43 to 0.74, with greater values in northern regions of low productivity where crop intensification is constrained by low temperature. SIGNIFICANCEThis analysis establishes smaller relative yields of OA than are commonly reported. Smaller yields per crop area in OA are further reduced at farm (system) level relative to CA by the larger proportion of land required in legume-based crops and pastures. Ruminant animals provide some compensation for that land by converting human-inedible fodder to human food. Consequently, transformation of CA farmland to OA would require additional land, up to 130% in productive southern and central regions, to maintain equal overall yield. More such comprehensive data are required for calculation of OA/CA yield ratios at the system level.

Giant sponge grounds of Central Arctic seamounts are associated with extinct seep life

The Central Arctic Ocean is one of the most oligotrophic oceans on Earth because of its sea-ice cover and short productive season. Nonetheless, across the peaks of extinct volcanic seamounts of the Langseth Ridge (87°N, 61°E), we observe a surprisingly dense benthic biomass. Bacteriosponges are the most abundant fauna within this community, with a mass of 460 g C m−2 and an estimated carbon demand of around 110 g C m−2 yr−1, despite export fluxes from regional primary productivity only sufficient to provide <1% of this required carbon. Observed sponge distribution, bulk and compound-specific isotope data of fatty acids suggest that the sponge microbiome taps into refractory dissolved and particulate organic matter, including remnants of an extinct seep community. The metabolic profile of bacteriosponge fatty acids and expressed genes indicate that autotrophic symbionts contribute significantly to carbon assimilation. We suggest that this hotspot ecosystem is unique to the Central Arctic and associated with extinct seep biota, once fueled by degassing of the volcanic mounts.

Amphibian body size and species richness as a proxy for primary productivity and climate: The Orce wetlands (Early Pleistocene, Guadix-Baza Basin, SE Spain)

Amphibians are considered excellent indicators of ecological and climatic changes with a remarkable phenotypic plasticity. The study of such adaptative capacities is central to understanding the climate and environmental changes that occurred during the Early-Middle Pleistocene Transition, at around 1.2 Ma, when the persistence of subtropical ecosystems in Europe came to an end, and several reptile and tree taxa were extirpated. The SE Spain sites in the Guadix-Baza Basin offer an exceptional opportunity for studying this change, in addition to the significant findings made in this area in the field of human evolution. We have analysed the body size of the most well-represented amphibian species in the sites, the Iberian waterfrog, Pelophylax perezi . In order to reconstruct past body sizes from fossil samples, a regression model from current osteological collections has been generated. Also, diversity of the herpetofauna community was studied at different levels as richness or species number. Finally, to study the relationships between body size, richness, climate and productivity, OLS regression models and Pearson correlations were applied. Also for this purpose, a productivity indicator was designed based on the addition of the two most productive ecosystems from previous habitat reconstruction. Amphibian body size appears to be negatively associated with primary productivity, reaching minimum values during the interglacial stages, when species richness increased. In contrast, during glacial periods characterised by greater aridity and fewer resources, amphibian body size increased while species richness decreased. Main explanations proposed to justify this pattern are the “water-availability hypothesis” and a trade-off between somatic growth and reproductive opportunities for females. The study of herpetofaunal diversity shows a clear correlation to regional plant diversity and primary productivity. The results of this work indicate that species richness and amphibian body size are valuable proxies that can complement current environmental and climate reconstruction methods. • Somatic growth and reproduction: the trade-off which determines amphibian body size. • Amphibian body size decreases towards more productive ecosystems. • Primary productivity determines species richness. • Frog body size is defined as a new indicator of Pleistocene ecosystem conditions.

Benthic foraminiferal assemblages and environmental drivers along the Kveithola Trough (NW Barents Sea)

We describe the population density, biodiversity and vertical distribution in the sediment of benthic foraminifera, and their relationship to environmental parameters, in the Kveithola Trough (NW Barents Sea). Two staining methods, Cell Tracker Green (CTG) and Rose Bengal (RB), were used to distinguish between living and dead tests. CTG proved to be more effective than RB, and we therefore used this approach to document faunal assemblage variability along a transect of the Trough. The outer shelf shows a diverse benthic foraminiferal assemblage suggesting an oxygenated and oligotrophic environment. The central part appears to be a disturbed area due to rapid circulation changes and organic matter burial in sediments where opportunistic foraminifera colonize only the first centimetres. In contrast, the inner part of the Trough seems to be a stressed environment where species associated with organic-rich sediment and oxygen-depleted environments dominate the living assemblage. At all sites, delicate monothalamids species form part of the assemblage. The peculiar geomorphological and environmental conditions of this area, and the high regional primary and secondary production, are key drivers of foraminiferal assemblage distribution. • This work analyses the living benthic foraminifera of the Kveithola Trough. • The peculiar conditions shape the living benthic foraminiferal structure. • Faunal distribution varies along the longitudinal transect of the area. • The main determining factor in the diversity is the organic matter concentration. • CTG method is appropriate to document the vitality of foraminifera in this area.

A modified two-leaf light use efficiency model for improving the simulation of GPP using a radiation scalar

Two-leaf light use efficiency (TL-LUE) models are efficient methods to simulate regional and global gross primary productivity (GPP). A TL-LUE model has previously been shown to outperform the big-leaf MOD17 model through separate consideration of the contributions of sunlit and shaded leaves. However, the impacts of radiation intensity on LUE are inadequately considered in the TL-LUE model, and the maximum LUEs of sunlit and shaded leaves are assigned as different constants, which often induce large uncertainties. Therefore, a TL-LUE model modified with a radiation scalar (RTL-LUE) is developed in this paper. The same maximum LUE is used for both sunlit and shaded leaves, and the difference in LUE between sunlit and shaded leaf groups is determined by the same radiation scalar. The RTL-LUE model was calibrated and validated at global 169 FLUXNET eddy covariance (EC) sites. Results indicate that although GPP simulations from the TL-LUE model match well with the EC GPP, the RTL-LUE model can further improve the simulation, for half-hour, 8-day, and yearly time scales. The TL-LUE model tends to overestimate GPP under conditions of high incoming photosynthetically active radiation (PAR), because the radiation-independent LUE values for both sunlit and shaded leaves are only suitable for low-medium (e.g., average) incoming PAR conditions. The errors in the RTL-LUE model show lower sensitivity to PAR, and its GPP simulations can better track the diurnal and seasonal variations of EC GPP by alleviating the overestimation at noon and growing seasons associated with the TL-LUE model. This study demonstrates the necessity of considering a radiation scalar in GPP simulation in LUE models even if the first-order effect of radiation is already considered through differentiating sunlit and shaded leaves. The simple RTL-LUE developed in this study would be a useful alternative to complex process-based models for global carbon cycle research.

The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts

Abstract. Filaments and fronts play a crucial role for a net offshore and downward nutrient transport in Eastern Boundary Upwelling Systems (EBUSs) and thereby reduce regional primary production. Most studies on this topic are based on either observations or model simulations, but only seldom are both approaches are combined quantitatively to assess the importance of filaments for primary production and nutrient transport. Here we combine targeted interdisciplinary shipboard observations of a cold filament off Peru with submesoscale-permitting (1/45∘) coupled physical (Coastal and Regional Ocean Community model, CROCO) and biogeochemical (Pelagic Interaction Scheme for Carbon and Ecosystem Studies, PISCES) model simulations to (i) evaluate the model simulations in detail, including the timescales of biogeochemical modification of the newly upwelled water, and (ii) quantify the net effect of submesoscale fronts and filaments on primary production in the Peruvian upwelling system. The observed filament contains relatively cold, fresh, and nutrient-rich waters originating in the coastal upwelling. Enhanced nitrate concentrations and offshore velocities of up to 0.5 m s−1 within the filament suggest an offshore transport of nutrients. Surface chlorophyll in the filament is a factor of 4 lower than at the upwelling front, while surface primary production is a factor of 2 higher. The simulation exhibits filaments that are similar in horizontal and vertical scale compared to the observed filament. Nitrate concentrations and primary production within filaments in the model are comparable to observations as well, justifying further analysis of nitrate uptake and subduction using the model. Virtual Lagrangian floats were released in the subsurface waters along the shelf and biogeochemical variables tracked along the trajectories of floats upwelled near the coast. In the submesoscale-permitting (1/45∘) simulation, 43 % of upwelled floats and 40 % of upwelled nitrate are subducted within 20 d after upwelling, which corresponds to an increase in nitrate subduction compared to a mesoscale-resolving (1/9∘) simulation by 14 %. Taking model biases into account, we give a best estimate for subduction of upwelled nitrate off Peru between 30 %– 40 %. Our results suggest that submesoscale processes further reduce primary production by amplifying the downward and offshore export of nutrients found in previous mesoscale studies, which are thus likely to underestimate the reduction in primary production due to eddy fluxes. Moreover, this downward and offshore transport could also enhance the export of fresh organic matter below the euphotic zone and thereby potentially stimulate microbial activity in regions of the upper offshore oxygen minimum zone.

The application of EO-1 Hyperion hyperspectral data to estimate the GPP of temperate forest in Changbai Mountain, Northeast China

Flux tower is a link between ground measurements and large-scale remote sensing data. A large number of remote sensing model methods are used to estimate the regional scale Gross Primary Productivity (GPP) based on this principle. In this study, Vegetation Photosynthesis Model (VPM) and Vegetation Indexes (VIs) were used to estimate the GPP based on Earth Observing 1 (EO-1) Hyperion hyperspectral data in Changbai Mountain temperate forest. Result shows that the two different types of remote sensing input data of the VPM has similar result at the same level. For different time scope, 3-day flux data can better match remote sensing data. For different footprint, the effect of 500, 1000, 1500 m almost no difference in our area. Among the comparison of the four types of VIs, Bands Ratio (BR), Bands Subtraction (BS) and Bands Difference (BD) have a higher correlation significant than Single Band (SB). 457 nm is the optimum band for SB. The best bands combination of BR, BS, and BD mainly focus on near infrared region. Our research shows that for VPM, and other Light Use Efficiency (LUE) remote sensing model, the difference is not significant between multispectral data and hyperspectral data. At the comparison of VPM and VIs, although the estimation of former is more accurate, the latter is more convenient for that the establishment of VIs just need several bands of remote sensing data. Our findings will help to improve future research on GPP estimation based on hyperspectral observations, which is being more important with increasing availability of hyperspectral satellite data products.

Observed variability in physical and biogeochemical parameters in the central Arabian Gulf

In situ measurements of physical and biogeochemical variables were conducted along a transect in the Exclusive Economic Zone (EEZ) of Qatar during late summer (September 2014) and winter (January 2015) to investigate their vertical, spatial and temporal variability. The study reveals that the water column is characterized by strong stratification during late summer in the deepest station, where the water depth is around 65 m and the surface to bottom temperature variation is around 9.1°C. The water column is vertically homogeneous during winter due to surface cooling and wind mixing. The surface to 23 m water column is characterized by ample dissolved oxygen (DO) during late summer and winter in the offshore regions, however, relatively low DO is found during late summer due to weak mixing and advection under weak winds and currents. Dissolved oxygen drops to hypoxic levels below the summer thermocline, and the winter high DO layer extends up to the bottom. Chlorophyll-a (Chl-a) is relatively high during late summer in the offshore region, while that in the nearshore regions is very low, which is linked to the anthropogenic stresses from the central east coast of Qatar. The results identified in this study fill an essential gap in the knowledge of regional primary production dynamics.

Growth of marine ectotherms is regionally constrained and asymmetric with latitude

AbstractAimGrowth rates of organisms are routinely used to summarize physiological performance, but the consequences of local evolutionary history and ecology are largely missed by analyses on wide biogeographical scales. This broad approach has been commonly applied to other physiological parameters across terrestrial and aquatic environments. Here, we examine growth rates of marine bivalves across all biogeographical realms, latitude, and temperature, with analyses to determine regional effects on growth on global scales.LocationGlobal: marine ecosystems.Time period1930–2018.Major taxaBivalves.MethodsWe use a comprehensive data set of bivalve growth parameters (n = 966, 243 species) representing all biogeographical realms to calculate overall growth performances. We use these data with environmental temperature to analyse global patterns in growth, accounting for regional primary productivity and phylogeny using general additive mixed and linear models. The Arrhenius relationship and corresponding activation energies are used to quantify the sensitivity to temperature in each biogeographical realm and province.ResultsOur analyses show that bivalve growth demonstrates latitudinal asymmetry and exhibits nonlinear relationships with latitude. We find that overall growth performance is affected by temperature and particulate organic carbon, but the form of these relationships differs with phylogeny. Growth is slower and more sensitive to increasing temperature in the Antarctic than it is in the Arctic, and decreases with increasing temperature in some tropical realms, a previously unidentified and fundamental difference in growth and physiological sensitivity.Main conclusionsOur findings provide compelling evidence that the widely used curvilinear relationship between temperature and growth rates in marine ectotherms is an inappropriate descriptor of thermal sensitivity, because it normalizes regional variations in physiological performance. Without a more detailed assessment of global physiological patterns, the responses of species to local variations associated with climate change will be under‐appreciated in global assessments of climate risk, minimizing the effectiveness of management and conservation.

A phosphate starvation response gene (psr1-like) is present and expressed in Micromonas pusilla and other marine algae

Phosphorus (P) limits primary production in regions of the surface ocean, and many plankton species exhibit specific physiological responses to P deficiency. The metabolic response of Micromonas pusilla, an ecologically relevant marine photoautotroph, to P deficiency was investigated using metabolomics and comparative genomics. The concentrations of some intracellular metabolites were elevated in the P-deficient cells (e.g. xanthine, inosine), and genes involved in the associated metabolic pathways shared a predicted conserved amino acid motif in the non-coding regions of each gene. The presence of the conserved motif suggests that these genes may be co-regulated, and the motif may constitute a regulatory element for binding a transcription factor, specifically that of Psr1 (phosphate starvation response). A putative phosphate starvation response gene (psr1-like) was identified in M. pusilla with homology to well characterized psr1/phr1 genes in algae and plants, respectively. This gene appears to be present and expressed in other marine algal taxa (e.g. Emiliania huxleyi) in field sites that are chronically P limited. Results from the present study have implications for understanding phytoplankton taxon-specific roles in mediating P cycling in the ocean.

Simulation of Enhanced Growth of Marine Group II Euryarchaeota From the Deep Chlorophyll Maximum of the Western Pacific Ocean: Implication for Upwelling Impact on Microbial Functions in the Photic Zone.

Mesoscale eddies can have a strong impact on regional biogeochemistry and primary productivity. To investigate the effect of the upwelling of seawater by western Pacific eddies on the composition of the active planktonic marine archaeal community composition of the deep chlorophyll maximum (DCM) layer, mesoscale cold-core eddies were simulated in situ by mixing western Pacific DCM layer water with mesopelagic layer (400 m) water. Illumina sequencing of the 16S rRNA gene and 16S rRNA transcripts indicated that the specific heterotrophic Marine Group IIb (MGIIb) taxonomic group of the DCM layer was rapidly stimulated after receiving fresh substrate from 400 m water, which was dominated by uncultured autotrophic Marine Group I (MGI) archaea. Furthermore, niche differentiation of autotrophic ammonia-oxidizing archaea (MGI) was demonstrated by deep sequencing of 16S rRNA, amoA, and accA genes, respectively. Similar distribution patterns of active Marine Group III (MGIII) were observed in the DCM layer with or without vertical mixing, indicating that they are inclined to utilize the substrates already present in the DCM layer. These findings underscore the importance of mesoscale cyclonic eddies in stimulating microbial processes involved in the regional carbon cycle.

Seasonal variability of near-surface zooplankton community structure in the southern Gulf of Mexico

The zooplankton taxonomic group composition was analyzed in a known spawning area for snooks of the family Centropomidae during March 2011-February 2012 near the González River's mouth, a tributary of the Grijalva-Usumacinta River system, discharging into the southern Gulf of Mexico. Zooplankton was collected near the surface using three distinct zooplankton nets (20, 64, and 120 μm). Sixteen zooplankton taxonomic groups were collected between the three nets. Copepoda (76.9%), Trematoda (6.7%), Bivalvia (4.6%), and Chaetognatha (Sagittoidea 4.3%) numerically dominated zooplankton community structure. The 120 and 64 μm nets collected the highest diversity of zooplankton (15 taxa). Zooplankton was more abundant during June-October (summer storm season). They associated with lower salinities (due to the increase in the discharge volume of the Grijalva-Usumacinta River system) and higher regional primary productivity than observed during the rest of the year (March-May, dry season, and November-February, winter storm season). The highest peak of zooplankton abundance was found in November during the beginning of winter storms. Nine taxonomic groups were observed frequently and abundantly during the summer storm season, while only five taxonomic groups were abundant during the dry season.

Changing Biogeochemistry of the Southern Ocean and Its Ecosystem Implications

The Southern Ocean plays a critical role in regulating global climate as a major sink for atmospheric carbon dioxide (CO2), and in global ocean biogeochemistry by supplying nutrients to the global thermocline, thereby influencing global primary production and carbon export. Biogeochemical processes within the Southern Ocean regulate regional primary production and biological carbon uptake, primarily through iron supply, and support ecosystem functioning over a range of spatial and temporal scales. Here we assimilate existing knowledge and present new data to examine the biogeochemical cycles of iron, carbon and major nutrients, their key drivers and their responses to, and roles in, contemporary climate and environmental change. Projected increases in iron supply, coupled with increases in light availability to phytoplankton through increased near-surface stratification and longer ice-free periods, are very likely to increase primary production and carbon export around Antarctica. Biological carbon uptake is likely to increase for the Southern Ocean as a whole, whilst there is greater uncertainty around projections of primary production in the Sub-Antarctic and basin-wide changes in phytoplankton species composition, as well as their biogeochemical consequences. Phytoplankton, zooplankton, higher trophic level organisms and microbial communities are strongly influenced by Southern Ocean biogeochemistry, in particular through nutrient supply and ocean acidification. In turn, these organisms exert important controls on biogeochemistry through carbon storage and export, nutrient recycling and redistribution, and benthic-pelagic coupling. The key processes described in this paper are summarised in the graphical abstract. Climate-mediated changes in Southern Ocean biogeochemistry over the coming decades are very likely to impact primary production, sea-air CO2 exchange and ecosystem functioning within and beyond this vast and critically important ocean region.

Organic geochemistry of a lacustrine shale across the Toarcian Oceanic Anoxic Event (Early Jurassic) from NE China

Thirty-nine shale samples of the Lower Jurassic Beipiao Formation from drill core ZK01 in the Jinyang Basin, NE China were investigated by comprehensive organic geochemical methods in this study. A prominent negative excursion in δ 13 C org values (~ 2‰) was observed in the Beipiao Formation, which is most likely associated with Toarcian Oceanic Anoxic Event (T-OAE) negative carbon isotope excursion (CIE) that is recorded globally in marine and terrestrial sediments constrained by previous studies. Elemental and Rock-Eval analyses of Beipiao shales demonstrate that the total organic carbon (TOC) ranges from 0.56 to 4.33 wt% (average of 1.40 wt%) and S 2 values range from 0.12 to 6.91 mg/g (average of 1.3 mg/g) and implicate fair to good source rock potential. A majority of the T max values of the Beipiao shales range from 456 to 465 °C, indicating that the organic matter is within the mature oil window apart from few overmature samples with extreme high T max values that might have been affected by local magmatic intrusions. Elemental analysis suggests that the kerogens are mainly Type II-III. Unlike many marine organic-rich sediments deposited during OAEs, redox proxies indicate no significant upper water column oxygen-depletion during the formation of Beipiao lacustrine shale. The decreasing upward trend of organic source indicators such as tricyclic terpanes/C 30 hopane values, relative distributions of regular C 27 steranes to C 29 steranes, and steranes/hopanes in the Beipiao Formation consistently suggest a shift to a lower abundance of eukaryotic organisms relative to bacterial community abundance during the onset of the T-OAE. Meanwhile, gradually decreasing values of gammacerane/C 30 hopane in the Beipiao Formation during the negative CIE suggest decreasing salinity and increased mixing of the Jinyang paleo-lake system, potentially corresponding with the shift toward an accelerated hydrological cycle with enhanced fresh water input to this lacustrine system. Moreover, increasing C 30 moretane/C 30 hopane values contemporaneous with the negative CIE also suggest enhanced land erosion during putative Toarcian climatic warming, which could have increased delivery of riverine nutrients and elevated regional primary productivity, eventually resulting in massive organic matter accumulation in the Beipiao shales. • A prominent negative excursion in δ 13 C org values (~ 2‰) was observed in the Toarcian Beipiao lacustrine shale. • A shift to lower abundance of eukaryote relative to bacterial community in lacustrine system during the onset of the T-OAE. • Progressive accelerated hydrological cycle enhanced fresh water input and increased mixing of NE China lacustrine system. • The organic enrichment and good hydrocarbon generation potential resulted from enhanced delivery of riverine nutrients.