Ocean Biogeochemical Fluxes - New Production And Export Of Organic-Matter From The Upper Ocean

Studies of ocean biogeochemical fluxes have been energized in this decade, by the urgency of our need to understand and predict the effects of continued CO2accumulation in the atmosphere, by the global perspectives offered by satellite views of ocean color and related physical fields (McClain et al. 1991; Yoder et al. 1992; Mitchell 1994), and by the successful implementation of the Joint Global Ocean Flux Study (JGOFS; Bowles and Livingston, 1993). In this review, I focus on oceanic new production, originally defined as the fraction of primary production supported by inputs of ‘new’ nitrogen from outside the euphotic zone. With a growing appreciation of the role of this fundamental biogeochemical flux in the global carbon cycle, it has become more common to refer interchangeably to new production so defined, and to the export of organic matter from the upper ocean (e.g.. Sarmiento and Siegenthaler 1992). New production, the driving process of the ocean carbon cycle, is responsible for maintaining over half the vertical gradient in total inorganic carbon. In this review I refer to nitrate‐based new production in the open sea, and not to new production supported by other N compounds as observed in the coastal zone. Eppley (1992) gives a personal view of the modern formulation of the concept of equivalence between new production and upper ocean export. This review is dedicated to the memory of John Martin, a friend, colleague, leader and teacher who contributed mightily to our field

Bacterioplankton growth responses to temperature and chlorophyll variations in estuaries measured by thymidine:leucine incorporation ratio

To identify the biochemical response of heterotrophic bacterioplankton to changing environmental conditions, seasonal and diel cycles of bacterial protein and DNA synthesis rates were estimated in temperate estuarine habitats from H-3-leucine (Leu) and H-3-thymidine (TdR) incorporation rates. Several short-term temperature manipulation experiments (5 to 35 degrees C) and 2 mesocosm experiments were performed to examine the effects of temperature and substrate supply on the ratio of Leu:TdR, respectively. The molar ratio of Leu to TdR varied about 5-fold (5.6 to 29.5) in the field and the values of the ratio were lower and more constant during high temperature (\u3e25 degrees C) and high chlorophyll a (\u3e8.0 mu g l(-1)) periods. In the temperature manipulation experiments, the Leu:TdR ratio decreased as temperature increased. In the mesocosm experiments, the Leu:TdR ratio was negatively correlated with chlorophyll a concentrations and bacterial specific growth rates. We propose that changes toward less favorable environmental conditions (e.g. reductions in temperature or substrate supply in temperate estuaries) might reduce bacterial protein and DNA synthesis rates simultaneously. However, the former process may be favored to maximize survival and this might lead to a higher Leu:TdR ratio. Conversely, when environmental conditions turn favorable, both processes could be enhanced and bacteria might optimize DNA duplication over protein metabolism to maximize reproduction, resulting in lower Leu:TdR ratios. Our results further indicate the complementariness of H-3-thymidine and H-3-leucine incorporation measurements for understanding processes controlling bacterial production since the ratio of these 2 tracer methods varied independently with temperature and substrate supply

Bacterioplankton distribution and production in the bathypelagic ocean: Directly coupled to particulate organic carbon export?

A recently published evaluation of bacterioplankton abundance and productivity in the bathypelagic North Pacific suggests that these properties are generally coupled with particulate organic carbon (POC) fluxes. In that analysis, bacterial biomass and productivity were several-fold greater in subarctic than subtropical waters, consistent with the basin-scale distribution of POC flux and suggestive of a sinking POC --\u3e DOC --\u3e bacteria transformation of the carbon. To test this hypothesis, we sought to determine whether the very strong spatial and temporal gradients in POC flux in the Arabian Sea would force similar deep-ocean gradients in bacterial variables. On both a within and between-cruise basis, there was variability in bacterial abundance and thymidine incorporation in the deep Arabian Sea, but correspondence was equivocal between these variables and several correlates to export: flux of biogenic carbon from the euphoric zone, state of the monsoon, and proximity to productive coastal upwelling zones. However, when annual mean bacterial abundance at 2,000 m was compared with annual POC flux at that depth, a strong correspondence emerged: high annual flux supported high bacterial abundance (such a correspondence was not found for bacterial productivity). This finding suggests that bathypelagic bacterial abundance responds to the long-term mean input of organic matter and less to episodic inputs. A comparative evaluation of the North Pacific revealed that although the bathypelagic bacteria there showed correspondence to deep POC flux, that variable alone would not account for the wide meridional variations in bacterial abundance that have been reported

Multiyear increases in dissolved organic matter inventories at station ALOHA in the North Pacific Subtropical Gyre

The inventories and dynamics of dissolved organic matter (DOM) in the surface water at Station ALOHA were analyzed from the Hawaii Ocean Time-series (HOT) data set for the period 1989-1999. Euphotic zone, depth-integrated (0-175 m) concentrations of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) were temporally variable. In particular, during the period 1993-1999, concentrations of DOC and DON increased while inventories of DOP remained unchanged. DOC inventories increased by 303 mmol C m(-2) yr(-1), a value equivalent to approximately 2% of measured primary production (C-14 method) at this site. DON increased at 11 mmol N m(-2) yr(-1), resulting in a mean molar DOC : DON ratio of 27.5 for the accumulated DOM. Accumulation of DOC and DON without corresponding accumulation of DOP resulted in changes to the bulk organic C : N : P stoichiometry; bulk DOC : DOP ratios increased 16% and DON: DOP ratios increased by 17%. These results indicate that a small fraction of the annually produced organic matter escaped biological utilization on time scales of months to years. More importantly, the accumulated DOM inventories grew progressively enriched in C and N relative to P. Fundamental changes in the North Pacific Subtropical Gyre (NPSG) habitat appear to have altered microbial processes that regulate organic matter fluxes. Considered together, the long-term increases in DOC and DON inventories are consistent with previous observations, indicating that a recent reorganization of plankton community dynamics may have altered organic matter cycling in this ecosystem

Light dependence of [H-3]leucine incorporation in the oligotrophic North Pacific ocean

The influence of irradiance on bacterial incorporation of [H-3] leucine was evaluated at Station ALOHA in the oligotrophic North Pacific subtropical gyre. Six experiments were conducted on three cruises to Station ALOHA to examine how [H-3]leucine incorporation varied as a function of irradiance. Two experiments were also conducted to assess the photoautotrophic response to irradiance (based on photosynthetic uptake of [C-14] bicarbonate) in both the upper and lower photic zones. Rates of [H-3]leucine incorporation responded to irradiance in a photosynthesis-like manner, increasing sharply at low light and then saturating and sometimes declining with increasing light intensity. The influence of irradiance on bacterial growth was evaluated in both the well-lit (5 to 25 m) and dimly lit regions of the upper ocean (75 to 100 m) to determine whether the bacterial response to irradiance differed along the depth-dependent light gradient of the photic zone. [H-3] leucine incorporation rates were analyzed with a photosynthesis-irradiance model for a quantitative description of the relationships between [H-3] leucine incorporation and irradiance. Maximum rates of [H-3] leucine incorporation in the upper photic zone increased 48 to 92% relative to those of dark-incubated samples, with [H-3]leucine incorporation saturating at light intensities between 58 and 363 mumol of quanta m(-2) s(-1). Rates of [H-3]Ieucine incorporation in the deep photic zone were photostimulated 53 to 114% and were susceptible to photoinhibition, with rates declining at light intensities of \u3e100 mumol of quanta m(-2) s(-1). The results of these experiments revealed that sunlight directly influences bacterial growth in this open-ocean ecosystem

Modeling distinct vertical biogeochemical structure of the Black Sea: Dynamical coupling of the oxic, suboxic, and anoxic layers

A one-dimensional, vertically resolved, physical-biogeochemical model is used to provide a unified representation of the dynamically coupled oxic-suboxic-anoxic system for the interior Black Sea. The model relates the annual cycle of plankton production in the form of a series of successive phytoplankton, mesozooplankton, and higher consumer blooms to organic matter generation and to the remineralization-ammonification-nitrification-dentrification chain of the nitrogen cycle as well as to anaerobic sulfide oxidation in the suboxic-anoxic interface zone. The simulations indicate that oxygen consumption during remineralixation and nitrification, together with a lack of ventilation of subsurface waters due to the presence of strong stratification, are the two main factors limiting aerobic biogeochemical activity to the upper similar to 75 m of the water column, which approximately corresponds to the level of nitrate maximum. The position of the upper boundary and thus the thickness of the suboxic layer are controlled by upper layer biological processes. The quasi-permanent character of this layer and the stability of the suboxic-anoxic interface within the last several decades are maintained by a constant rate of nitrate supply from the nitrate maximum zone. Nitrate is consumed to, oxidize sinking particulate organic matter as well as hydrogen sulfide and ammonium transported upward from deeper levels

Climatic warming and accompanying changes in the ecological regime of the Black Sea during 1990s

The Black Sea ecosystem is shown to experience abrupt shifts in its all trophic levels from primary producers to apex predators in 1995 - 1996. It arises as a manifestation of concurrent changes in its physical climate introduced by intensive warming of its surface waters as well as abrupt increases in the mean sea level and the net annual mean fresh water flux. The warming is evident in the annual-mean sea surface temperature (SST) data by a continuous rise at a rate of similar to 0.25 degreesC per year, following a strong cooling phase in 1991 - 1993. The most intense warming event with similar to2 degreesC increase in the SST took place during winters of the 1994 - 1996 period. It also coincides with 4 cm yr(-1) net sea level rise in the basin, and substantial change in the annual mean net fresh water flux from 150 km(3) yr(-1) in 1993 to 420 km(3) yr(-1) in 1997. The subsurface signature of warming is marked by a gradual depletion of the Cold Intermediate Layer ( characterized by T \u3c 8 °C) throughout the basin during the same period. Winters of the warming phase are characterized by weaker vertical turbulent mixing and upwelling velocity, stronger stratification and, subsequently, reduced upward nutrient supply from the nutricline. From 1996 onward, the major late winter-early spring peak of the classical annual phytoplankton biomass structure observed prior to mid- 90s was, therefore, either weakened or disappeared altogether depending on local meteorological and oceanographic conditions during each of these years. The effect of bottom-up limited unfavorable phytoplankton growth is reflected at higher trophic levels (e.g., mesozooplankton, gelatinous macrozooplankton, and pelagic fishes) in the form of their reduced stocks after 1995

Melting glaciers: A probable source of DDT to the Antarctic marine ecosystem

Persistent organic pollutants reach polar regions by long-range atmospheric transport and biomagnify through the food web accumulating in higher trophic level predators. We analyzed Adelie penguin (Pygoscelis adeliae) samples collected from 2004 to 2006 to evaluate current levels of Sigma DDT (p,p\u27-DDT + p,p\u27-DDE) in these birds, which are confined to Antarctica. Ratios of p,p\u27-DDT to p,p\u27-DDE in Adelie penguins have declined significantly since 1964 indicating current exposure to old rather than new sources of Sigma DDT. However, Sigma DDT has not declined in Adelie penguins from the Western Antarctic Peninsula for more than 30 years and the presence of p,p\u27-DDT in these birds indicates that there is a current source of DDT to the Antarctic marine food web. DDT has been banned or severely restricted since peak use in the 1970s, implicating glacier meltwater as a likely source for DDT contamination in coastal Antarctic seas. Our estimates indicate that 1-4 kg.y(-1) Sigma DDT are currently being released into coastal waters along the Western Antarctic Ice Sheet due to glacier ablation

Growth dynamics of Phaeocystis antarctica-dominated plankton assemblages from the Ross Sea

Large-volume experiments were conducted using natural seawater assemblages collected in the southern Ross Sea during austral spring 1994 and summer 1995 to assess the carbon and nitrogen exchanges among phytoplankton, bacteria and dissolved organic carbon pools, and to compare the elemental partitioning in these experimental enclosures with those observed in situ. Large concentrations of particulate matter were produced in these enclosures, which were at all times dominated by the colonial haptophyte Phaeocystis antarctica. Particulate organic carbon concentrations exceeded 200 mu mol l(-1) at the end of the experiment. Bacterial carbon comprised only a small (%) fraction of the particulate carbon, but bacteria grew at 0.15 to 0.3 d(-1) and were not limited by bacteriovores. Nutrient levels decreased concomitantly with POC increases, and nitrate was reduced to undetectable levels. Dissolved organic carbon (DOC) levels remained low (less than 50 mu M) while nutrients were present, but increased dramatically (to more than 200 mu M) after nitrate was depleted. Growth rates calculated from changes in particulate matter concentrations were slightly below the predicted maximum based on temperature. Field studies, however, showed no depletion of nitrate, similar levels of particulate organic carbon to those found during exponential growth, low levels of DOG, and relatively low levels of bacterial biomass. It appears that P. antarctica in the Ross Sea does not produce large amounts of DOC during nutrient-replete growth; furthermore, because macronutrients are rarely, if ever, depleted where P. antarctica is dominant in the Ross Sea, it is likely that much of the carbon generated during its growth remains in the particulate pool

Responses of Antarctic Marine and Freshwater Ecosystems to Changing Ice Conditions

Polar regions are warming more rapidly than lower latitudes, and climate models predict that this trend will continue into the coming decades. Despite these observations and predictions, relatively little is known about how polar ecosystems have responded and will continue to respond to this change. Two Long-Term Ecological Research (LTER) sites, located in contrasting environments in Antarctica, have been studying marine and aquatic terrestrial ecosystems for more than two decades. We use data from these research areas to show that the extent and thickness of ice covers are highly sensitive to short- and long-term climate variation and that this variation significantly influences ecosystem processes in these respective environments. Declining sea-ice extent and duration diminishes phytoplankton blooms as a consequence of reduced water stratification, whereas the thinning of lake-ice cover enhances phytoplankton blooms because of increased penetrating light into the water column. Both responses have cascading effects on upper trophic levels