Positive Net Community Production Research Articles

Seasonal and interannual variability of the pelagic ecosystem and of the organic carbon budget in the Rhodes Gyre (eastern Mediterranean): influence of winter mixing

Abstract. The Rhodes Gyre is a cyclonic persistent feature of the general circulation of the Levantine Basin in the eastern Mediterranean Sea. Although it is located in the most oligotrophic basin of the Mediterranean Sea, it is a relatively high primary production area due to strong winter nutrient supply associated with the formation of Levantine Intermediate Water. In this study, a 3D coupled hydrodynamic–biogeochemical model (SYMPHONIE/Eco3M-S) was used to characterize the seasonal and interannual variability of the Rhodes Gyre's ecosystem and to estimate an annual organic carbon budget over the 2013–2020 period. Comparisons of model outputs with satellite data and compiled in situ data from cruises and Biogeochemical-Argo floats revealed the ability of the model to reconstruct the main seasonal and spatial biogeochemical dynamics of the Levantine Basin. The model results indicated that during the winter mixing period, phytoplankton first progressively grow sustained by nutrient supply. Then, short episodes of convection driven by heat loss and wind events, favoring nutrient injections, organic carbon export, and inducing light limitation on primary production, alternate with short episodes of phytoplankton growth. The estimate of the annual organic carbon budget indicated that the Rhodes Gyre is an autotrophic area, with a positive net community production in the upper layer (0–150 m) amounting to 31.2 ± 6.9 gCm-2yr-1. Net community production in the upper layer is almost balanced over the 7-year period by physical transfers, (1) via downward export (16.8 ± 6.2 gCm-2yr-1) and (2) through lateral transport towards the surrounding regions (14.1 ± 2.1 gCm-2yr-1). The intermediate layer (150–400 m) also appears to be a source of organic carbon for the surrounding Levantine Sea (7.5 ± 2.8 gCm-2yr-1) mostly through the subduction of Levantine Intermediate Water following winter mixing. The Rhodes Gyre shows high interannual variability with enhanced primary production, net community production, and exports during years marked by intense heat losses and deep mixed layers. However, annual primary production appears to be only partially driven by winter vertical mixing. Based on our results, we can speculate that future increase of temperature and stratification could strongly impact the carbon fluxes in this region.

Artificial Upwelling in Singular and Recurring Mode: Consequences for Net Community Production and Metabolic Balance

Artificial upwelling of nutrient-rich waters and the corresponding boost in primary productivity harbor the potential to enhance marine fishery yields and strengthen the biological pump for sequestration of atmospheric CO2. There is increasing urgency to understand this technology as a “ocean-based solution” for counteracting two major challenges of the 21st century—climate change and overfishing. Yet, little is known about the actual efficacy and/or possible side effects of artificial upwelling. We conducted a large-scale off-shore mesocosm study (∼44 m3) in the oligotrophic waters of the Canary Islands to identify the community-level effects of artificial upwelling on a natural oligotrophic plankton community. Four upwelling intensities were simulated (approx. 1.5/3/5.7/10 μmol L–1 of nitrate plus phosphate and silicate) via two different upwelling modes (a singular deep-water pulse vs. recurring supply every 4 days) for 37 days. Here we present results on the response of net community production (NCP), metabolic balance and phytoplankton community composition (<250 μm). Higher upwelling intensities yielded higher cumulative NCP. Following upwelling onset, the phytoplankton community became dominated by diatoms in all treatments, but other taxa such as Coccolithophores increased later in the experiment. The magnitude of effects on the metabolic balance scaled with the amount of added deep water, leading to (i) a balanced to net-heterotrophic system in the singular and (ii) a net-autotrophic system in the recurring upwelling treatments. Accordingly, the mode in which nutrients are supplied to an oligotrophic system plays a crucial role in the ecosystem response, with recurring upwelling leading to higher long-term positive NCP than singular upwelling. These results highlight the importance of empirically measured local responses to upwelling such as community structure and metabolism, with major implications for the potential employment of artificial upwelling as an ocean-based solution to generate (primary) production.

Controls on the Fate of Dissolved Organic Carbon Under Contrasting Upwelling Conditions

To understand controls on the production and remineralization of recalcitrant dissolved organic carbon produced in association with positive net community production, we simulated upwelling systems of different intensities by combining and incubating whole seawater collected from different depths in the Florida Strait (27˚N, ~79˚W). The natural microbial communities in the treatments grew under controlled light and temperature for 15 days (i.e., the autotrophic phase); they were subsequently incubated for 35 days in the dark heterotrophic phase. We analyzed the phytoplankton composition and pigment fluorescence intensity during the light phase, and dissolved organic and inorganic variables during both phases. Initial high or low availability of inorganic nutrients controlled phytoplankton growth and the magnitude of NCP. In the strong upwelling treatment, with higher initial inorganic nutrients, 25% of NCP accumulated as DOC after 15 days; however, this material was in turn fully remineralized during the dark phase. In contrast, low nutrients in the weak upwelling treatment not only limited NCP, but also the fraction of NCP accumulated as DOC (11%). Surprisingly, most of this fraction resisted microbial remineralization in the dark phase, suggesting that upwellings of different intensities affect the quality of dissolved organic matter produced, thereby affecting the timing and location of its remineralization and, hence, its prospects for export to the deep ocean.

Carbonate system parameters of an algal-dominated reef along West Maui

Abstract. Constraining coral reef metabolism and carbon chemistry dynamics are fundamental for understanding and predicting reef vulnerability to rising coastal CO2 concentrations and decreasing seawater pH. However, few studies exist along reefs occupying densely inhabited shorelines with known input from land-based sources of pollution. The shallow coral reefs off Kahekili, West Maui, are exposed to nutrient-enriched, low-pH submarine groundwater discharge (SGD) and are particularly vulnerable to the compounding stressors from land-based sources of pollution and lower seawater pH. To constrain the carbonate chemistry system, nutrients and carbonate chemistry were measured along the Kahekili reef flat every 4 h over a 6-day sampling period in March 2016. Abiotic process – primarily SGD fluxes – controlled the carbonate chemistry adjacent to the primary SGD vent site, with nutrient-laden freshwater decreasing pH levels and favoring undersaturated aragonite saturation (Ωarag) conditions. In contrast, diurnal variability in the carbonate chemistry at other sites along the reef flat was driven by reef community metabolism. Superimposed on the diurnal signal was a transition during the second sampling period to a surplus of total alkalinity (TA) and dissolved inorganic carbon (DIC) compared to ocean endmember TA and DIC measurements. A shift from positive net community production and positive net community calcification to negative net community production and negative net community calcification was identified. This transition occurred during a period of increased SGD-driven nutrient loading, lower wave height, and reduced current speeds. This detailed study of carbon chemistry dynamics highlights the need to incorporate local effects of nearshore oceanographic processes into predictions of coral reef vulnerability and resilience.

Net community production and carbon export during the late summer in the Ross Sea, Antarctica

AbstractThe phytoplankton bloom in the Ross Sea is the largest in spatial extent and one of the most productive in Antarctica, yet the fate of the summer bloom remains poorly understood. Here we present carbon system data from the first biogeochemical process cruise to be conducted in both the western and central Ross Sea during late summer (February–March 2013). Using one‐dimensional carbon budgets, we found evidence for substantial positive net community production (425 ± 204 mmol C m−2 d−1) during the late summer in Terra Nova Bay (TNB) of the western Ross Sea, which was rapidly exported to below 200 m. In addition, seasonally integrated carbon export was higher in diatom‐dominated TNB (7.3 ± 0.9 mol C m−2) compared to the Phaeocystis antarctica‐dominated central Ross Sea (3.4 ± 0.8 mol C m−2). Substantial late summer productivity and export may be a widespread phenomenon in Antarctic coastal regions that is not accounted for in regional carbon models.

Ocean glider observations of iceberg‐enhanced biological production in the northwestern Weddell Sea

AbstractIcebergs affect local biological production around Antarctica. We used an ocean glider to observe the effects of a large iceberg that was advected by the Antarctic Slope Current along the continental slope in the northwestern Weddell Sea in early 2012. The high‐resolution glider data reveal a pronounced effect of the iceberg on ocean properties, with oxygen concentrations of (13 ± 4) μmol kg−1 higher than levels in surrounding waters, which are most likely due to positive net community production. This response was confined to three areas of water in the direct vicinity of the iceberg track, each no larger than 2 km2. Our findings suggest that icebergs have an impact on Antarctic production presumably through local micronutrient injections, on a scale smaller than typical satellite observations of biological production in the Southern Ocean.

Plankton community and bacterial metabolism in Arctic sea ice leads during summer 2010

Microbial plankton metabolism was examined during summer 2010 in sea ice-influenced waters of the Fram Strait, eastern Arctic Ocean. Rates of gross primary production and community respiration were tightly coupled over a wide range of values (33±3–143±6 and 20±3–126±6mmol O2m−2−1, respectively) leading to a prevalence of positive net community production. The high variability in community respiration, similar to that of gross primary production, suggests that heterotrophic metabolism may exhibit a significant response to environmental change. Bacterial respiration was assessed at similar time scales to bacterial production measurements, by determining the in vivo INT reduction capacity without pre-filtering the community. Bacteria seem to play a major role in total community respiration, contributing between 5% and 61% of total community respiration, indicating that a high fraction of the organic carbon in Arctic planktonic food webs could flow through these microbes.

The Oligotrophic Ocean Is Autotrophic

In vitro observations of net community production (NCP) imply that the oligotrophic subtropical gyres of the open ocean are net heterotrophic; in situ observations, in contrast, consistently imply that they are net autotrophic. At least one approach must be returning an incorrect answer. We find that (a) no bias in in situ oxygen-based production estimates would give false-positive (net autotrophy) rates, (b) observed (13)C enrichment of surface water dissolved inorganic carbon (DIC) can be explained only by positive NCP (net autotrophy), (c) lateral and vertical inputs of organic carbon are insufficient to sustain net heterotrophy, and (d) atmospheric input of organic material is too small to support in vitro rates of net heterotrophy and would yield δ(13)C depletion of surface DIC, quite the opposite of what is observed in the subtropical gyres. We conclude that the in vitro observations, implying net heterotrophy, must contain a bias that is due to an underestimate of photosynthetic rate and/or an overestimate of respiration rate.

Influence of seasonal monsoons on net community production and CO<sub>2</sub> 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.

Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 62:1-12 (2011) - DOI: https://doi.org/10.3354/ame01451 FEATURE ARTICLE Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean Donn A. Viviani, Karin M. Björkman, David M. Karl, Matthew J. Church* Department of Oceanography, University of Hawaii, Honolulu, Hawaii 96822, USA *Corresponding author. Email: mjchurch@hawaii.edu ABSTRACT: We measured plankton metabolism and evaluated changes in plankton community structure within the central Pacific Ocean during a trans-equatorial cruise from the South Pacific Subtropical Gyre (SPSG) to the North Pacific Subtropical Gyre (NPSG). Rates of net community production (NCP) and respiration (R) were determined in near-surface ocean waters, based on light–dark bottle measurements of oxygen production and consumption. Gross primary production (GPP) was computed, where GPP = NCP + R. Rates of GPP and R in the oligotrophic SPSG and NPSG were tightly coupled, resulting in NCP that was either zero or slightly negative. These subtropical waters were characterized by very low concentrations of inorganic nutrients (e.g. nitrate+nitrite range: 0.004 to 0.033 µmol l–1). Within the relatively nutrient-enriched equatorial waters (e.g. nitrate+nitrite concentrations range: 0.67 to 5.7 µmol l–1), GPP exceeded R by up to 5-fold, resulting in positive NCP. GPP varied ~16-fold (0.25 to 4.05 µmol O2 produced l–1 d–1) while R varied ~5-fold (0.31 to 1.56 µmol O2 consumed l–1 d–1). Picoplankton cell abundances and diagnostic pigment biomarkers were used to determine regional differences in phytoplankton community structure. In the near-equatorial waters, abundances of Synechococcus and photosynthetic picoeukaryotes increased up to 100- and 10-fold, respectively, and diagnostic pigment biomarkers for eukaryotic phytoplankton (including diatoms, pelagophytes, and haptophytes) also increased. These results indicate that variability in nutrient availability constitutes an important regulator of net productivity and plankton community structure in large regions of the open ocean. KEY WORDS: Gross primary production · Respiration · Net community production · Equatorial Pacific · Subtropical gyres Full text in pdf format Information about this Feature Article NextCite this article as: Viviani DA, Björkman KM, Karl DM, Church MJ (2011) Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean. Aquat Microb Ecol 62:1-12. https://doi.org/10.3354/ame01451 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 62, No. 1. Online publication date: January 04, 2011 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2011 Inter-Research.

The carbon dioxide system and net community production within a cyclonic eddy in the lee of Hawaii

Abstract The dynamics of dissolved inorganic carbon (DIC) and processes controlling net community production (NCP) were investigated within a mature cyclonic eddy, Cyclone Opal , which formed in the lee of the main Hawaiian Islands in the subtropical North Pacific Gyre. Within the eddy core, physical and biogeochemical properties suggested that nutrient- and DIC-rich deep waters were uplifted by ∼80 m relative to surrounding waters, enhancing biological production. A salt budget indicates that the eddy core was a mixture of deep water (68%) and surface water (32%). NCP was estimated from mass balances of DIC, nitrate+nitrite, total organic carbon, and dissolved organic nitrogen, making rational inferences about the unobserved initial conditions at the time of eddy formation. Results consistently suggest that NCP in the center of the eddy was substantially enhanced relative to the surrounding waters, ranging from 14.1±10.6 (0–110 m: within the euphotic zone) to 14.2±9.2 (0–50 m: within the mixed layer) to 18.5±10.7 (0–75 m: within the deep chlorophyll-maximum layer) mmol C m −2 d −1 depending on the depth of integration. NCP in the ambient waters outside the eddy averaged about 2.37±4.24 mmol C m −2 d −1 in the mixed layer (∼0–95 m). Most of the enhanced NCP inside the eddy appears to have accumulated as dissolved organic carbon (DOC) rather than exported as particulate organic carbon (POC) to the mesopelagic. Our results also suggest that the upper euphotic zone (0–75 m) above the deep chlorophyll maximum is characterized by positive NCP, while NCP in the lower layer (>75 m) is close to zero or negative.

The metabolic balance of the planktonic community in the North Atlantic Subtropical Gyre: The role of mesoscale instabilities

We have studied the net community production (NCP) balance in the Eastern region of the Subtropical North Atlantic during two cruises, in August 1998 and April 1999. In August, heterotrophic bacteria were more abundant than picophytoplankton, which resulted in net heterotrophy (NCP = –129 mmol O2 m−2 d−1 ± 18; mean ± SE), whereas these differences in plankton components were not apparent in April 1999, when the community was in metabolic balance (NCP = –13 mmol O2 m−2 d−1 ± 19). In April, the metabolic balance of microplankton communities was net heterotrophic outside (NCP = –57 mmol O2 m−2 d−1 ± 26) and lower than inside (NCP = 19 mmol O2 m−2 d−1 ± 19) the mesoscale structures present in the area (subtropical front, cyclonic eddy Leticia, and the Great Meteor Tablemount). Positive NCP inside the cyclonic eddy (NCP = 20 mmol O2 m−2 d−1 ± 17) was due to lower respiration rather than to higher gross primary production rates. Gross extrapolation suggests that the regional organic carbon deficit within the Eastern Subtropical Gyre (0.98–1.88 Gt C yr−1) should increase by ~14% and 52% in the absence of mesoscale structures.

Dissolved inorganic carbon, alkalinity, nutrient and oxygen seasonal and interannual variations at the Antarctic Ocean JGOFS-KERFIX site

JGOFS-KERFIX (KERguelen point FIXe) time-series station, located south of the polar front in the Indian sector of the Antarctic Ocean, was occupied monthly between January 1990 and March 1995. Annual cycles of dissolved inorganic carbon (DIC), total alkalinity (TALK), oxygen (O 2) and nutrients (nitrate, silicate, phosphate and ammonia) in the upper ocean are presented for this site. From seasonal drawdown of nutrients and DIC, we estimate a spring–summer net community production of 3.2±0.5 mol m −2 and C/N/P ratios of 100/16/1. The Si/N ratio varies between 1.8 and 3, suggesting low iron concentrations. The spring–summer biogenic silicon export derived from silicate drawdown is 1.18 mol m −2, consistent with model estimates of silicate export at this site. Seasonal and interannual variations of oxygen, nitrate and DIC due to physical and biological processes are quantified using a simple month-to-month budget formulation. From these budgets, an annual net community production of 5.7±3.3 mol m −2 yr −1 is estimated, about twice the averaged spring–summer production, indicating that, at KERFIX, there is a positive net community production throughout the year. Air–sea CO 2 fluxes show that KERFIX is a strong CO 2 sink for the atmosphere of 2.4–5.1 mol m −2 yr −1 in 1993, depending on the gas exchange formulation used. A 2.1–3.3 mol m −2 yr −1 outgassing of O 2 is observed at KERFIX except in 1993 and 1994 where a decreasing trend of temperature induces an increase of O 2 solubility.

Bacteria—protist interactions and organic matter degradation under P‐limited conditions: Analysis of an enclosure experiment using a simple model

An enclosure experiment was performed in the brackish layer of a Norwegian fjord, a system where both phytoplankton and bacterial growth have previously been hypothesized to be phosphorus (p) limited. All enclosures had a succession pattern characterized by an initial autotrophic phase with positive net community production, increasing phytoplankton primary production, and chlorophyll, followed by a heterotrophic phase with decline in primary production, negative net community production, increased community respiration, bacterial production, and biomass. Daily additions of phosphate increased the amplitudes of both the autotrophic and the heterotrophic phases of this succession. Because no stimulating effect of glycine addition on bacterial production or on community respiration was observed, the delay in bacterial response could not easily be explained as a delay in production or availability of carbon substrates for the bacteria. An alternative hypothesis is that bacterial production is regulated by a combination of P‐limited bacterial growth rate and predatory control of bacterial biomass. A simple numerical model based on this hypothesis was able to reproduce the main features of the observed pattern of succession.

Seasonal compensation of microbial production and respiration in a temperate sea

Gross oxygen production (GP), dark respiration (DR) and net community production (NCP) were studied for 16 mo in the euphotic layer of 3 stations through the coastal transitional zone of the southern Bay of Biscay, and related to hydrographic and nutrient conditions, phytoplankton biomass and C incorporation. Microbial O 2 fluxes exhibited seasonal patterns linked to the seasonal cycle of water column stratification and mixing, with positive NCP during the spring, negative throughout the summer and close to zero in winter. This pattern was altered at coastal regions, where productive periods were linked to coastal upwelling, whereas in winter persistent net heterotrophy was measured, presumably in relation to increases in organic matter discharge of continental origin. The comparison of NCP with O 2 anomaly and NO 3 concentration in the euphotic zone, the spatial and temporal scales studied and the prevalence of steady-state conditions offshore support the conclusion that the maintenance of summer heterotrophy in the region was based upon the consumption of the surplus of organic matter produced in spring. The uncoupling in the microbial auto- and heterotrophic metabolisms, based on the accumulation and delayed consumption of dissolved organic matter as a consequence of the processes controlling phytoplankton growth and microbial heterotrophic activity in temperate seas, would explain such a pattern. The close relationship observed between the seasonal variability in NCP and the magnitude of spring net production and predictions derived from the seasonal cycles of O 2 anomaly in middle latitudes and atmospheric O 2 led us to conclude that the seasonal compensation of production and respiration processes is a characteristic of the dynamics of the pelagic ecosystem, at least in coastal temperate seas. The implications of this conclusion are of great relevance for the interpretation of new production and the estimation of the trophic status of the ocean from direct measurements of plankton net production.

Primary production and community respiration in a warm streamer associated with Kuroshio warm core ring in spring

Daily rates of gross primary production, net community production and community respiration were determined in spring of 1997 at two stations in a warm streamer off Sanriku, Japan fromin vitro changes in dissolved oxygen. The phytoplankton community was composed of chlorophytes, cryptophytes and prymnesiophytes as determined by biomarker pigment analysis. Gross production, integrated from the surface to its 1% light level was 52.5 and 80.4 mmol O2 m−2d−1. The difference in gross production is ascribed to variations in photosynthetic activity of the population. Community respiration was 17.4 and 49.5 mmol O2 m−2d−1, and positive net community production was found within the euphotic zone. The contribution of autotrophic and heterotrophic respiration to community respiration was estimated on the basis of the observed respiration and the phytoplankton composition. Heterotrophic respiration was calculated to be highly variable and the observed difference in community respiration was due to heterotrophic respiration. Heterotrophic respiration was considered to play an important role in the rapid mineralization of organic materials.

Metabolism and carbon exchange in microplankton of the Grand Banks (Newfoundland)

We measured simultaneously the size-distribution of oxygen consumption, inorganic and orgamc dissolved carbon assimilation, and the standing stocks of phytoplankton and bacteria, to develop simple carbon budgets and C exchange models for the microplankton communities of a large conhnental shelf system. In spring samples (dominated by large-celled dlatoms) community respiration consumed 33 to 100 % or more of the gross primary production (GPP) measured by the 0,-light-anddark-bottle technique and was apparently due entirely to microheterotrophs. In fall samples (dominated by flagellates) community respiration consumed 100 % or more of the measured GPP, and appeared on average to be due equally to autotrophs and heterotrophs. Pnmary production, estimated by 14C-CO2 assimilation into particulate matter, often greatly underestimated GPP and community metabolism measured by the 0, technique, with apparent photosynthetic quotients (PQ) of about 5.0 in the spring samples. Modelling of the tracer dynamics suggested large rates of DOC release (> particulate production) from a small and rapidly cycling pool w i t h the autotrophs as the cause of the large apparent PQ's. The large share of primary production consumed by small microheterotrophs ( c 5 or l p) and frequent lack of positive net community production suggested a low efficiency for the transfer of microheterotrophic production to larger or.;a~isn?s.