Estimation of phytoplankton production from space: current status and future potential of satellite remote sensing

A new generation of ocean colour satellites is now operational, with frequent observation of the global ocean. This paper reviews the potential to estimate marine primary production from satellite images. The procedures involved in retrieving estimates of phytoplankton biomass, as pigment concentrations, are discussed. Algorithms are applied to SeaWiFS ocean colour data to indicate seasonal variations in phytoplankton biomass in the Celtic Sea, on the continental shelf to the south west of the UK. Algorithms to estimate primary production rates from chlorophyll concentration are compared and the advantages and disadvantage discussed. The simplest algorithms utilise correlations between chlorophyll concentration and production rate and one equation is used to estimate daily primary production rates for the western English Channel and Celtic Sea; these estimates compare favourably with published values. Primary production for the central Celtic Sea in the period April to September inclusive is estimated from SeaWiFS data to be 102 gC m⁻² in 1998 and 93 gC m⁻² in 1999; published estimates, based on in situ incubations, are ca. 80 gC m⁻². The satellite data demonstrate large variations in primary production between 1998 and 1999, with a significant increase in late summer in 1998 which did not occur in 1999. Errors are quantified for the estimation of primary production from simple algorithms based on satellite-derived chlorophyll concentration. These data show the potential to obtain better estimates of marine primary production than are possible with ship-based methods, with the ability to detect short-lived phytoplankton blooms. In addition, the potential to estimate new production from satellite data is discussed.     

Growth and mortality rates of phytoplankton in the northwestern North Pacific estimated by the dilution method and HPLC pigment analysis

Pigment-based growth rates of phytoplankton and mortality rates due to microzooplankton grazing were estimated using a dilution method combined with high-performance liquid chromatography (HPLC) pigment analysis in the northwestern North Pacific in autumn 1998. The dilution experiments were conducted at different hydrographic stations in both colder and warmer water masses. No significant difference was found between the growth rate of the phytoplankton community (0.38–0.70 day⁻¹; estimated by chlorophyll a) at the colder and warmer water stations, while the mortality rate (0.15–0.88 day⁻¹; estimated by chlorophyll a) tended to be higher at warmer water stations. The combination of estimates of daily chlorophyll a production and particulate organic carbon (POC) production enabled us to assess the carbon to chlorophyll a ratio (C/chl a) of “new” organic matter produced by living phytoplankton. The method provided an implicit value of the C/chl a of in situ living phytoplankton. The rate estimates from taxon-specific pigments suggested a possibility that chlorophyll b-containing green algae were grazed preferentially by microzooplankton during their active growth, and the standing stock of green algae was more strictly controlled by micrograzer than other algal groups such as diatoms. This result is one possible explanation for the fact that blooms of green algae have not been reported in the open ocean, in contrast with diatoms.     

Primary production under hypertrophic conditions and its relationship with bacterial production

In shallow hypertrophic lakes where light availability restricts the growth of macrophytes and benthic phytoplankton, pelagic phytoplankton modulates importantly ecosystem production and the energy transfer to heterotrophic bacteria. Diel and seasonal variations in primary production (PP) were studied in the hypertrophic Albufera de Valencia (Spain). Additionally, the relationship between PP and heterotrophic bacterial production (BP) was assessed. PP was extremely high, exceeding most values reported for hypertrophic lakes to date. PP displayed marked diurnal variations defined by the solar radiation curve. Likewise, PP changed importantly across seasons. Minimum PP coincided with maximum water transparency and short water residence times in winter, whereas maximum PP was observed in late spring associated with high chlorophyll a. The spring PP maximum contrasted with the summer maximum often observed in hypertrophic lakes. When compared to spring PP values, summer PP values were lower as a result of strong nitrogen limitation. In contrast to PP, BP remained fairly constant across seasons. Nonetheless, there was a joint diminution during increased water transparency followed by an increase in early spring. Phytoplankton was always the most relevant input to particulate carbon production, but the BP/PP ratio showed clear seasonal variations. The BP/PP ratio was minimum in spring, low in summer and highest in winter. The extracellular dissolved organic carbon released by phytoplankton was sufficient to meet bacterial carbon demand in all experimental dates, suggesting that allochthonous carbon sources play a minor role in sustaining BP, though they cannot be excluded. However, we hypothesize that high availability of dissolved organic carbon might explain the lack of coupling observed between BP and PP.     

The freshwater tidal wetland Liberty Island,CA was both a source and sink of inorganic and organic material to the San Francisco Estuary

It is hypothesized that perennial freshwater tidal wetland habitat exports inorganic and organic material needed to support the estuarine food web and to create favorable habitat for aquatic organisms in San Francisco Estuary. It is also hypothesized that most of the material flux in this river-dominated region is controlled by river flow. The production and export of material by Liberty Island were measured and compared using discrete monthly and continuous (15 min) measurements of a suite of inorganic and organic materials and flow between 2004 and 2005. Seasonal material flux was estimated from monthly discrete data for inorganic nutrients, suspended solids and salts, organic carbon and nitrogen and phytoplankton and zooplankton group carbon and chlorophyll a and pheophytin pigment. Estimates of material flux from monthly values were compared with measured daily material flux values for chlorophyll a concentration, salt and suspended solids obtained from continuous measurements (15 min) using YSI water quality sondes. Phytoplankton carbon produced within the wetland was estimated by in situ primary productivity. Most inorganic and organic materials were exported from the wetland on an annual basis, but the magnitude and direction varied seasonally. Dissolved inorganic nutrients such as nitrate, soluble phosphorus, total phosphorus and silica as well as total suspended solids were exported in the summer while total and dissolved organic carbon were exported in the winter. Salts like chloride and bromide were exported in the fall. Chlorophyll a and pheophytin were exported in the fall and associated with diatom and cyanobacteria carbon. Mesozooplankton carbon was dominated by calanoid copepods and exported most of the year except summer. Continuous sampling revealed high hourly and daily variation in chlorophyll a, salt and total suspended solids flux due to high frequency changes in concentration and tidal flow. In fact, tidal flow rather than river discharge was responsible for 90% or more of the material flux of the wetland. These studies indicate that freshwater tidal wetlands can be a source of inorganic and organic material but the export of material is highly variable spatially and temporally, varies most closely with tidal flow and requires high frequency measurements of both tidal flow and material concentration for accurate estimates.     

Pigment patterns in suspended matter from the Elbe estuary,Northern Germany

In the Elbe hardly anything is known about the actual fate of phytoplankton and the resultant pigment composition of suspended matter. As part of a longterm study on the role of suspended matter in the cycles of nitrogen and associated oxygen consumption processes in the Elbe estuary in northern Germany (‘Sonderforschungsbereich 327 Elbe’ project) and the characterization of estuarine and coastal water bodies with regard to the transport of pollutants such as heavy metals, we have started to characterize suspended matter with regard to the pigments present therein. This will allow us to study phytoplankton turnover and to determine the role of phytoplankton decay mechanisms in the mobilization, binding, and transport of pollutants associated with particulate matter. Our first data on the pigment composition of suspended matter from the Elbe and particularly over the region of Hamburg harbour, obtained using a High Performance Liquid Chromatography (HPLC) method, is presented. The pigment concentrations varied considerably over the summer months. Values up to 250 mg l⁻¹ of chlorophyll a were observed upstream of Hamburg. We found that on its course through Hamburg the concentrations (μg g⁻¹ of particulate matter) of all pigments in the Elbe drop to under half those found upstream of Hamburg. The pigment concentrations in the turbidity maximum were significantly lower than in the rest of the estuary due to the decline of algae as a result of inadequate light conditions and the salinity gradient. The highest particulate matter concentrations were found in the turbidity maximum and just downstream of Hamburg. The highest particulate organic carbon values were found just downstream of Hamburg. The presence of of fucoxanthin and the chlorophyllsc andb, and the changes in pigment patterns were indicative for the dominant algal classes and the phytoplankton succession in the suspended matter. The ratio of chlorophylla to lutein was found to be a possible indicator of phytoplankton breakdown.     

Oceanic sinks for atmospheric CO2

There is approximately 50 times more inorganic carbon in the global ocean than in the atmosphere. On time scales of decades to millions of years, the interaction between these two geophysical fluids determines atmospheric CO₂ levels. During glacial periods, for example, the ocean serves as the major sink for atmospheric CO₂, while during glacial–interglacial transitions, it is a source of CO₂ to the atmosphere. The mechanisms responsible for determining the sign of the net exchange of CO₂ between the ocean and the atmosphere remain unresolved. There is evidence that during glacial periods, phytoplankton primary productivity increased, leading to an enhanced sedimentation of particulate organic carbon into the ocean interior. The stimulation of primary production in glacial episodes can be correlated with increased inputs of nutrients limiting productivity, especially aeolian iron. Iron directly enhances primary production in high nutrient (nitrate and phosphate) regions of the ocean, of which the Southern Ocean is the most important. This trace element can also enhance nitrogen fixation, and thereby indirectly stimulate primary production throughout the low nutrient regions of the central ocean basins. While the export flux of organic carbon to the ocean interior was enhanced during glacial periods, this process does not fully account for the sequestration of atmospheric CO₂. Heterotrophic oxidation of the newly formed organic carbon, forming weak acids, would have hydrolyzed CaCO₃ in the sediments, increasing thereby oceanic alkalinity which, in turn, would have promoted the drawdown of atmospheric CO₂. This latter mechanism is consistent with the stable carbon isotope pattern derived from air trapped in ice cores. The oceans have also played a major role as a sink for up to 30% of the anthropogenic CO₂ produced during the industrial revolution. In large part this is due to CO₂ solution in the surface ocean; however, some, poorly quantified fraction is a result of increased new production due to anthropogenic inputs of combined N, P and Fe. Based on ‘circulation as usual’, models predict that future anthropogenic CO₂ inputs to the atmosphere will, in part, continue to be sequestered in the ocean. Human intervention (large-scale Fe fertilization; direct CO₂ burial in the deep ocean) could increase carbon sequestration in the oceans, but could also result in unpredicted environmental perturbations. Changes in the oceanic thermohaline circulation as a result of global climate change would greatly alter the predictions of C sequestration that are possible on a ‘circulation as usual’ basis.     

Cascading influence of inorganic nitrogen sources on DOM production,composition, lability and microbial community structure in the open ocean

Nitrogen frequently limits oceanic photosynthesis and the availability of inorganic nitrogen sources in the surface oceans is shifting with global change. We evaluated the potential for abrupt increases in inorganic N sources to induce cascading effects on dissolved organic matter (DOM) and microbial communities in the surface ocean. We collected water from 5 m depth in the central North Pacific and amended duplicate 20 liter polycarbonate carboys with nitrate or ammonium, tracking planktonic carbon fixation, DOM production, DOM composition and microbial community structure responses over 1 week relative to controls. Both nitrogen sources stimulated bulk phytoplankton, bacterial and DOM production and enriched Synechococcus and Flavobacteriaceae; ammonium enriched for oligotrophic Actinobacteria OM1 and Gammaproteobacteria KI89A clades while nitrate enriched Gammaproteobacteria SAR86, SAR92 and OM60 clades. DOM resulting from both N enrichments was more labile and stimulated growth of copiotrophic Gammaproteobacteria (Alteromonadaceae and Oceanospirillaceae) and Alphaproteobacteria (Rhodobacteraceae and Hyphomonadaceae) in weeklong dark incubations relative to controls. Our study illustrates how nitrogen pulses may have direct and cascading effects on DOM composition and microbial community dynamics in the open ocean.     

Evolved physiological responses of phytoplankton to their integrated growth environment

Phytoplankton growth and productivity relies on light, multiple nutrients and temperature. These combined factors constitute the 'integrated growth environment'. Since their emergence in the Archaean ocean, phytoplankton have experienced dramatic shifts in their integrated growth environment and, in response, evolved diverse mechanisms to maximize growth by optimizing the allocation of photosynthetic resources (ATP and NADPH) among all cellular processes. Consequently, co-limitation has become an omnipresent condition in the global ocean. Here we focus on evolved phytoplankton populations of the contemporary ocean and the varied energetic pathways they employ to solve the optimization problem of resource supply and demand. Central to this discussion is the allocation of reductant formed through photosynthesis, which we propose has the following three primary fates: carbon fixation, direct use and ATP generation. Investment of reductant among these three sinks is tied to cell cycle events, differentially influenced by specific forms of nutrient stress, and a strong determinant of relationships between light-harvesting (pigment), photosynthetic electron transport and carbon fixation. Global implications of optimization are illustrated by deconvolving trends in the 10-year global satellite chlorophyll record into contributions from biomass and physiology, thereby providing a unique perspective on the dynamic nature of surface phytoplankton populations and their link to climate.     

Identifying the dominant process (physical versus biological) in pelagic marine ecosystems from field estimates of chlorophyll a and phytoplankton production

A new approach is described to identify the dominant process (physical versus biological) in a pelagic marine ecosystem, from simple biological oceanographic field variables. The approach is based on quantification of the matching (M) between phytoplankton production (P) and losses, from field estimates of chlorophyll a(Chl) and P. Coefficient M is estimated for a wide range of oceanic and coastal environments and of trophic characteristics, using dat from the literature. Results show that M characterizes the dominance of physical versus biological processes in pelagic systems. The coefficient may be especially useful as a means for extracting process information on pelagic marine ecosystems from large data sets of Chl and P, e.g. recorded by moored instruments or provided by satellite images of ocean colour.      

The significance of extracellular production and winter photosynthesis to estimates of primary production in a woodland stream community

Both winter photosynthesis and the release of extracellular DOC are commonly ignored in stream production studies. We examined these contributions in a second-order stream under a completely closed deciduous canopy. We estimate that in Sandy Run approximately 26% of the annual autochthonous particulate carbon is produced between December and March. Measured winter rates of photosynthesis were not significantly different than summertime rates. Contrary to implicit assumptions often made about stream primary productivity, winter production was as important as summer production. Highest rates of carbon assimilation, however, were measured in the spring and fall, and were significantly correlated with standing crops of stream algae as measured by chlorophyll concentration. The recovery of released DOC from stream algae indicated that this contribution was equivalent to 5% of the particulate contribution. Rates of DOC production were significantly correlated with rates of particulate production. We estimate that had winter photosynthesis and extracellular DOC production been ignored in Sandy Run, annual productivity would have been underestimated by about a third. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development and ecological importance of phytoplankton in a large lowland river (River Meuse,Belgium)

The ecological importance of the River Meuse phytoplankton with regard to carbon and nutrient transport has been examined in two reaches of the Belgian course of the river.Field measurements of total particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) show that the large autochtonous production of organic matter strongly affects the carbon and nutrient budget of the aquatic system. During the growing season, phytoplankton accounts for nearly 60% of the POC and dominates the PON. Calculations of the carbon and oxygen budget in the upper reach of the Belgian Meuse demonstrates that the ecosystem is autotrophic, i.e. that autochtonous FPOM (fine particulate organic matter) production is the major carbon input. This suggests that in large lowland rivers, primary production (P) may exceed community respiration (R), i.e. P:R>1, whereas they are assumed to be heterotrophic (P:R<1) in the River Continuum concept.The question of maintenance of phytoplankton in turbid mixed water columns is also addressed, and the case of the River Meuse is treated on the basis of studies of photosynthesis and respiration (ETS measurements). The results suggest that the potamoplankton may show some low-light acclimation, through an increase of chlorophyll a relative to biomass, when it comes to deep downstream reaches, and that algal respiration rate may be reduced. A simulation of the longitudinal development of the algal biomass shows the different phases of algal growth and decline along the river and brings support to the importation hypothesis for explaining maintenance of potamoplankton in the downstream reaches.     

The annual cycles of phytoplankton biomass

Terrestrial plants are powerful climate sentinels because their annual cycles of growth, reproduction and senescence are finely tuned to the annual climate cycle having a period of one year. Consistency in the seasonal phasing of terrestrial plant activity provides a relatively low-noise background from which phenological shifts can be detected and attributed to climate change. Here, we ask whether phytoplankton biomass also fluctuates over a consistent annual cycle in lake, estuarine–coastal and ocean ecosystems and whether there is a characteristic phenology of phytoplankton as a consistent phase and amplitude of variability. We compiled 125 time series of phytoplankton biomass (chlorophyll a concentration) from temperate and subtropical zones and used wavelet analysis to extract their dominant periods of variability and the recurrence strength at those periods. Fewer than half (48%) of the series had a dominant 12-month period of variability, commonly expressed as the canonical spring-bloom pattern. About 20 per cent had a dominant six-month period of variability, commonly expressed as the spring and autumn or winter and summer blooms of temperate lakes and oceans. These annual patterns varied in recurrence strength across sites, and did not persist over the full series duration at some sites. About a third of the series had no component of variability at either the six- or 12-month period, reflecting a series of irregular pulses of biomass. These findings show that there is high variability of annual phytoplankton cycles across ecosystems, and that climate-driven annual cycles can be obscured by other drivers of population variability, including human disturbance, aperiodic weather events and strong trophic coupling between phytoplankton and their consumers. Regulation of phytoplankton biomass by multiple processes operating at multiple time scales adds complexity to the challenge of detecting climate-driven trends in aquatic ecosystems where the noise to signal ratio is high.     

Carbon flux between an estuary and the ocean: a case for outwelling

The classical outwelling hypothesis states that small coastal embayments (e.g. estuaries, wetlands) export their excess production to inshore marine waters. In line with this notion, the present study tested whether the Swartkops estuary acts as source or sink for carbon. To this end, concentrations of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and particulate organic carbon (POC) were determined hourly during the first monthly spring and neap tides over one year in the tidal waters entering and leaving the estuary. Each sampling session spanned a full tidal cycle, yielding a total of 936 concentration estimates. Carbon fluxes were calculated by integrating concentrations with water flow rates derived from a hydrodynamic model calibrated for each sampling datum. Over the year, exports to marine waters markedly exceeded imports to the estuary for all carbon species: on the basis of total spring tidal drainage area, 1083 g m^–2 of DIC, 103 g m^–2 of DOC, and 123 g m^–2 of POC left the estuary annually. Total carbon export from the estuary to the ocean amounted to 4755 tonnes, of which 83% was in the inorganic form (DIC). Thus, the bulk of carbon moving in the water column is inorganic - yet, DIC seems to be measured only rarely in most flux studies of this nature. Salt marshes cover extensive areas in this estuary and produce some carbon, particularly DOC, but productivity of the local Spartina species is low (P:B=1.1). Consequently, the bulk of carbon exported from the estuary appears to originate from the highly productive macroinvertebrate and the phytoplankton component and not from the salt marsh plants.     

Spatial and temporal photosynthetic compartments during summer in Antarctic Lake Kitiesh

Summary Four autotrophic compartments were recognised in Lake Kitiesh, King George Island (Southern Shetland) at the beginning of the summer in 1987: snow microalgae, ice bubble communities, phytoplankton in the water column and benthic communities of moss with epiphytes. Chlorophyll a concentration and pigment absorption spectra were obtained in these four compartments before and/or after the thawing of the ice cover. During the ice free period, carbon fixation and biomass was measured in the phytoplankton and in the benthic moss Campyliadelphus polygamus. From these measurements we conclude that the benthic moss is the most significant autotrophic component in this lake in terms of biomass, chlorophyll a content and primary productivity. The integral assimilation number (The ratio of carbon fixation per unit area to biomass per unit area) values were similar for both phytoplankton and the moss, ranging from 3.6 to 5.4 mg C (mg Chl a)^–1h^–1in phytoplankton and from 4.0 to 6.4 mgC (mg Chl a)^–1h^–1 in the benthic moss. This approach allows comparisons of carbon fixation efficiency of the chlorophyll a under a unit area between compartments in their different light environments.     

Phytoplankton production and growth rate in Lake Tanganyika: evidence of a decline in primary productivity in recent decades

1. This study focused on phytoplankton production in Lake Tanganyika. We provide new estimates of daily and annual primary production, as well as growth rates of phytoplankton, and we compare them with values published in former studies.
2. Chlorophyll- a (chl- a ) in the mixed layer ranged from 5 to 120 mg chl- a  m⁻² and varied significantly between rainy and dry seasons. Particulate organic carbon concentrations were significantly higher in the south basin (with 196 and 166 mg C m⁻³ in the dry and the rainy season, respectively) than in the north basin (112 and 109 mg C m⁻³, respectively).
3. Carbon : phosphorus (C : P) ratios varied according to season. Phosphorus limitation seemed to occur more frequently than nitrogen limitation, especially during the rainy season. Severe P deficiencies were rare.
4. Measured particulate daily primary production ranged from 110 to 1410 mg C m⁻² day⁻¹; seasonal contrasts were well marked in the north basin, but less in the south basin, where primary production peaks occurred also in the rainy season. Estimates of annual primary production, based on daily primary production calculated from chl- a and water transparency, gave values lower than those reported in previous studies. Picophytoplankton accounted on average for 56% of total particulate production in the south basin during the wet season of 2003.
5. Phytoplankton growth rates, calculated from primary production, ranged from 0.055 to 0.282 day⁻¹; these are lower than previously published values for Lake Tanganyika.     

Spatial and temporal variability in export fluxes of biogenic matter in Kongsfjorden

The marine ecosystem of Kongsfjorden experiences large variations in primary productivity due to pronounced seasonal variations in sunlight, glacier melt, and ice cover. The objective of this study was to assess spatial and seasonal variability in the downward export of biogenic matter in Kongsfjorden. Short-term sediment traps were deployed for periods ranging from 21 to 52 h at three stations from the inner fjord to the outer fjord in May, August, and October 2012 and at one mid-fjord station in January 2013. Total particulate matter, particulate organic carbon, phytoplankton cells, chlorophyll a, biogenic particulate silica, and zooplankton fecal pellet fluxes were measured to determine the magnitude and composition of the material exported in the fjord. The amount and composition of export fluxes reflected a large phytoplankton bloom grazed upon by zooplankton in May, the melting of glaciers and the intrusion of Atlantic Water in August, the end of the glacier melt period in October, and the polar night in January. Overall, seasonal changes in the phytoplankton community impacted export efficiency in the fjord, directly through phytoplankton sinking and indirectly through zooplankton grazing. Results obtained in this study may reflect the magnitude and composition of export fluxes to expect in coming years in Kongsfjorden, especially under conditions of warmer Atlantic Water and longer glacier melt periods.     

Seasonality of chlorophyll and nutrients in Lake Erken – effects of weather conditions

The effect of submerged macrophytes on interactions among epilimnetic phosphorus, phytoplankton, and heterotrophic bacterioplankton has been acknowledged, but remains poorly understood. Here, we test the hypotheses that the mean summer phytoplankton biomass (chlorophyll a): phosphorus ratios decrease with increased macrophyte cover in a series of nine lakes. Further, we test that both planktonic respiration and bacterioplankton production increase with respect to phytoplankton biomass along the same gradient of increasing macrophyte cover. Increased macrophyte cover was associated with a lower fraction of particulate phosphorus in epilimnia, with total particulate phosphorus declining from over 80% of total phosphorus in a macrophyte free lake to less than 50% in a macrophyte rich lake. Phytoplankton biomass (chlorophyll a) too was lower in macrophyte dominated lakes, despite relatively high levels of total dissolved phosphorus. Planktonic respiration and bacterioplankton production were higher in macrophyte rich lakes than would be expected from phytoplankton biomass alone, pointing to a subsidy of bacterioplankton metabolism by macrophyte beds at the whole lake scale. The results suggest that the classical view of pelagic interactions, which proposes phosphorus determines phytoplankton abundance, which in turn determines bacterial abundance through the production of organic carbon, becomes less relevant as macrophyte cover increases.     

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

The partitioning of organic matter (OM) between dissolved and particulate phases is an important factor in determining the fate of organic carbon in the ocean. Dissolved organic matter (DOM) release by phytoplankton is a ubiquitous process, resulting in 2–50% of the carbon fixed by photosynthesis leaving the cell. This loss can be divided into two components: passive leakage by diffusion across the cell membrane and the active exudation of DOM into the surrounding environment. At present there is no method to distinguish whether DOM is released via leakage or exudation. Most explanations for exudation remain hypothetical; as while DOM release has been measured extensively, there has been relatively little work to determine why DOM is released. Further research is needed to determine the composition of the DOM released by phytoplankton and to link composition to phytoplankton physiological status and environmental conditions. For example, the causes and physiology of phytoplankton cell death are poorly understood, though cell death increases membrane permeability and presumably DOM release. Recent work has shown that phytoplankton interactions with bacteria are important in determining both the amount and composition of the DOM released. In response to increasing CO₂ in the atmosphere, climate change is creating increasingly stressful conditions for phytoplankton in the surface ocean, including relatively warm water, low pH, low nutrient supply and high light. As ocean physics and chemistry change, it is hypothesized that a greater proportion of primary production will be released directly by phytoplankton into the water as DOM. Changes in the partitioning of primary production between the dissolved and particulate phases will have bottom-up effects on ecosystem structure and function. There is a need for research to determine how these changes affect the fate of organic matter in the ocean, particularly the efficiency of the biological carbon pump.