Edward A. Laws

Temperature effects on export production in the open ocean

A pelagic food web model was formulated with the goal of developing a quantitative understanding of the relationship between total production, export production, and environmental variables in marine ecosystems. The model assumes that primary production is partitioned through both large and small phytoplankton and that the food web adjusts to changes in the rate of allochthonous nutrient inputs in a way that maximizes stability, i.e., the ability of the system to return to steady state following a perturbation. The results of the modeling exercise indicate that ef ratios, defined as new production/total production = export production/total production, are relatively insensitive to total production rates at temperatures greater than ∼25°C and lie in the range 0.1-0.2. At moderate to high total production rates, ef ratios are insensitive to total production and negatively correlated with temperature. The maximum ef ratios are ∼0.67 at high rates of production and temperatures of 0°−10°C. At temperatures less than ∼20°C, there is a transition from low ef ratios to relatively high ef ratios as total production increases from low to moderate values. This transition accounts for the hyperbolic relationship often presumed to exist between ef ratios and total production. At low rates of production the model predicts a negative correlation between production and ef ratios, a result consistent with data collected at station ALOHA (22°45′N, 158°W) in the North Pacific subtropical gyre. The predictions of the model are in excellent agreement with results reported from the Joint Global Ocean Flux Study (JGOFS) and from other field work. In these studies, there is virtually no correlation between total production and ef ratios, but temperature alone accounts for 86% of the variance in the ef ratios. Model predictions of the absolute and relative abundance of autotrophic and heterotrophic microorganisms are in excellent agreement with data reported from field studies. Combining the ef ratio model with estimates of ocean temperature and photosynthetic rates derived from satellite data indicates that export production on a global scale is ∼20% of net photosynthesis. The results of the model have important implications for the impact of climate change on export production, particularly with respect to temperature effects.

Dependence of phytoplankton carbon isotopic composition on growth rate and [CO2)aq: Theoretical considerations and experimental results

The carbon isotopic composition of the marine diatom Phaeodactylum tricornutum (δ13Cp) was measured over a series of growth rates (μ) in a continuous culture system in which both δ133CCO2 and [CO2]aq were determined. In accord with theory, a linear relationship was found to exist between μ/ [CO2]aq and ɛp (≡1000(δ13CCO2 − δ13Cp)/1000 + d δ13Cp), the biological fractionation associated with carbon fixation. The range of [CO2]aq in the continuous culture system was 13–31 μmol kg−1. Measurements of δ13CCO2 and [CO2]aq in the mixed layer of the equatorial Pacific and estimates of δ13Cp obtained from the δ13C of chlorophyll a combined with the regression line fit to the P. tricornutum data give phytoplankton growth rates that are in excellent agreement with those estimated via other techniques. Measurement of ɛp and [CO2]aq in the field can provide an estimate of in situ phytoplankton growth rates without the potential artifacts associated with incubation methodologies. These findings also suggest that accurate estimations of ancient CO2(aq) concentrations will require knowledge of both ɛp and phytoplankton growth rate.

Effect of Phytoplankton Cell Geometry on Carbon Isotopic Fractionation

The carbon isotopic compositions of the marine diatom Porosira glacialis and the marine cyanobacterium Synechococcus sp. were measured over a series of growth rates (μ) in a continuous culture system in which the concentration and carbon isotopic composition of CO2(aq) were determined. These data were compared with previously published isotopic results of growth rate experiments using the marine diatom Phaeodactylum tricornutum and the marine haptophyte Emiliania huxleyi. Systematic relationships were found to exist between μ/[CO2(aq)] and carbon isotopic fractionation (ϵP) for each species. Maximum isotopic fractionation (ϵf) for P. glacialis, E. huxleyi, and P. tricornutum was ∼25‰, suggesting that this value may be typical for maximum fractionation associated with Rubisco and β-carboxylases for marine eukaryotic algae. By contrast, ϵf determined for Synechococcus clone CCMP838 was ∼7‰ lower. The slopes of the lines describing the relationship between ϵP and μ/[CO2(aq)] for eukaryotic algal species were different by a factor of more than 20. This result can be accounted for by differences in the surface area and cellular carbon content of the cells. Comparison of chemostat experimental results with calculated results using a diffusion based model imply that the algae in the experiments were actively transporting inorganic carbon across the cell membrane. Our results suggest that accurate estimates of paleo-[CO2(aq)] from ϵP measured in sediments will require knowledge of growth rate as well as cell surface area and either cell carbon quota or cell volume. Given growth rate estimates, our empirical relationship permits reliable calculations of paleo-[CO2(aq)] using compound-specific isotopic analyses of C37 alkadienones (select haptophytes) or fossilized frustules (diatoms).

Photosynthetic quotients, new production and net community production in the open ocean

Abstract Based on balanced chemical equations for the production of proteins, polysaccharides, lipids and nucleic acids from inorganic precursors and reported estimates of the composition of microalgal biomass, the photosynthetic quotients (PQs) for new and recycled production are estimated to be 1.4 ± 0.1 and 1.1 ± 0.1, respectively. Reports that the PQs for new production is 1.8 or higher appear to result from comparisons of gross oxygen production to net CO2 assimilation. Available experimental data suggest that net community carbon production and new production of carbon in the ocean differ by less than 10%. Evidence indicates that the ratio of carbon to nitrogen (C:N) in the organic matter exported from the photic zone exceeds the Redfield ratio of 5.7 by weight, regardless of whether the organic matter is exported in the form of dissolved organics or passively or actively transported particulates. Hence scaling nitrate uptake by the Redfield ratio to estimate net community carbon production will tend to underestimate the export of organic carbon from the photic zone, the magnitude of the probable error being roughly 15–30%.

Primary productivity and particle fluxes on a transect of the equator at 153°W in the Pacific Ocean

Abstract Primary productivity (14C) and mass flux measurements using a free-drifting sediment trap deployed at 900 m were made at four stations in the Pacific Ocean between 12°N and 6°S at 153°W. The latitudinal variations in productivity were consistent with historical patterns showing the equator as a zone of high production and the oligotrophic waters north of the equatorial region as an area of low productivity. The correlation coefficient between the two sets of independent measurements was 0.999, indicating that in this oceanic area the activity of the primary producers was closely related to the total mass flux. A re-examination of historical data suggests that the downward flux of particulate organic carbon varies in direct proportion to the quotient of surface primary production raised to the 1.4 power and depth raised to the 0.63 power.

Consistent fractionation of 13C in nature and in the laboratory: Growth‐rate effects in some haptophyte algae

The carbon isotopic fractionation accompanying formation of biomass by alkenone-producing algae in natural marine environments varies systematically with the concentration of dissolved phosphate. Specifically, if the fractionation is expressed by epsilon p approximately delta e - delta p, where delta e and delta p are the delta 13C values for dissolved CO2 and for algal biomass (determined by isotopic analysis of C37 alkadienones), respectively, and if Ce is the concentration of dissolved CO2, micromole kg-1, then b = 38 + 160*[PO4], where [PO4] is the concentration of dissolved phosphate, microM, and b = (25 - epsilon p)Ce. The correlation found between b and [PO4] is due to effects linking nutrient levels to growth rates and cellular carbon budgets for alkenone-containing algae, most likely by trace-metal limitations on algal growth. The relationship reported here is characteristic of 39 samples (r2 = 0.95) from the Santa Monica Basin (six different times during the annual cycle), the equatorial Pacific (boreal spring and fall cruises as well as during an iron-enrichment experiment), and the Peru upwelling zone. Points representative of samples from the Sargasso Sea ([PO4] < or = 0.1 microM) fall above the b = f[PO4] line. Analysis of correlations expected between mu (growth rate), epsilon p, and Ce shows that, for our entire data set, most variations in epsilon p result from variations in mu rather than Ce. Accordingly, before concentrations of dissolved CO2 can be estimated from isotopic fractionations, some means of accounting for variations in growth rate must be found, perhaps by drawing on relationships between [PO4] and Cd/Ca ratios in shells of planktonic foraminifera.

Appropriate use of regression analysis in marine biology

The Model I linear regression theory is often used in the analysis of data under conditions when the Model II theory is clearly needed. Implications derived from the use of the two theories can differ greatly when there is not a high degree of correlation between the X and Y variables. The geometric mean Model II method is easy to use, and is probably needed in the analysis of most field data, since the X variable in field data is rarely under the control of the investigator.

Impacts of climate variability and future climate change on harmful algal blooms and human health.

Anthropogenically-derived increases in atmospheric greenhouse gas concentrations have been implicated in recent climate change, and are projected to substantially impact the climate on a global scale in the future. For marine and freshwater systems, increasing concentrations of greenhouse gases are expected to increase surface temperatures, lower pH, and cause changes to vertical mixing, upwelling, precipitation, and evaporation patterns. The potential consequences of these changes for harmful algal blooms (HABs) have received relatively little attention and are not well understood. Given the apparent increase in HABs around the world and the potential for greater problems as a result of climate change and ocean acidification, substantial research is needed to evaluate the direct and indirect associations between HABs, climate change, ocean acidification, and human health. This research will require a multidisciplinary approach utilizing expertise in climatology, oceanography, biology, epidemiology, and other disciplines. We review the interactions between selected patterns of large-scale climate variability and climate change, oceanic conditions, and harmful algae.

The 2007 water crisis in Wuxi, China: analysis of the origin.

An odorous tap water crisis that affected two million residents for several days occurred in Wuxi, China in the summer of 2007. Volatile sulfide chemicals including methyl thiols, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide were the dominant odorous contaminants in Lake Taihu and in tap water during the crisis. These contaminants originated from the decomposition of a massive cyanobacterial bloom that was triggered by illegal industrial discharges and inadequately regulated domestic pollution. A specific emergency drinking water treatment process was quickly developed using a combination of potassium permanganate oxidation and powdered activated carbon adsorption. The emergency treatment process removed the odor from the tap water and solved the crisis successfully in several days. This experience underscores the suggestion that a combination of stresses associated with eutrophication and industrial and domestic wastewater discharges can push an aquatic system to the tipping point with consequences far more severe than would occur if the system were subjected to each stress separately.

Atmospheric iron inputs and primary productivity: Phytoplankton responses in the North Pacific

As part of the Asian Dust Inputs to the Ocean System (ADIOS) project, atmospheric dust fluxes and primary productivity were monitored during the dusty season (spring) of 1986 at 26°N, 155°W, in the North Pacific Ocean. The arrival of major pulses of dust from Asia was followed by major increases in primary production. Extensive chemical analyses of the atmospheric particles showed that they were iron-rich (10-15%) and, further, that if only a small proportion (e.g. 10%) of this iron dissolved in the euphotic zone, it would be sufficient to support the increases in carbon production at this location. The systematic increases in production noted with increasing depth and time may result from a continual release of iron from the settling particles in the euphotic zone. At all depths, systematic decreases in production followed the initial surge in production, indicating that the phytoplankton may have evolved from being iron-limited to being nitrogen-limited. Comparison of particle concentrations calculated by a particle settling model with primary productivity profiles indicated that mineral particles with settling velocities equivalent to those of 14 to 18-μm-diameter spherical quartz particles were the most likely source for the iron stimulating the increases in primary production.