Beschreibung: In this paper, we review the state of the art and major challenges in current efforts to incorporate biogeochemical functional groups into models that can be applied on basin-wide and global scales, with an emphasis on models that might ultimately be used to predict how biogeochemical cycles in the ocean will respond to global warming. We define the term “biogeochemical functional group” to refer to groups of organisms that mediate specific chemical reactions in the ocean. Thus, according to this definition, “functional groups” have no phylogenetic meaning—these are composed of many different species with common biogeochemical functions. Substantial progress has been made in the last decade toward quantifying the rates of these various functions and understanding the factors that control them. For some of these groups, we have developed fairly sophisticated models that incorporate this understanding, e.g. for diazotrophs (e.g. Trichodesmium), silica producers (diatoms) and calcifiers (e.g. coccolithophorids and specifically Emiliania huxleyi). However, current representations of nitrogen fixation and calcification are incomplete, i.e., based primarily upon models of Trichodesmium and E. huxleyi, respectively, and many important functional groups have not yet been considered in open-ocean biogeochemical models. Progress has been made over the last decade in efforts to simulate dimethylsulfide (DMS) production and cycling (i.e., by dinoflagellates and prymnesiophytes) and denitrification, but these efforts are still in their infancy, and many significant problems remain. One obvious gap is that virtually all functional group modeling efforts have focused on autotrophic microbes, while higher trophic levels have been completely ignored. It appears that in some cases (e.g., calcification), incorporating higher trophic levels may be essential not only for representing a particular biogeochemical reaction, but also for modeling export. Another serious problem is our tendency to model the organisms for which we have the most validation data (e.g., E. huxleyi and Trichodesmium) even when they may represent only a fraction of the biogeochemical functional group we are trying to represent. When we step back and look at the paleo-oceanographic record, it suggests that oxygen concentrations have played a central role in the evolution and emergence of many of the key functional groups that influence biogeochemical cycles in the present-day ocean. However, more subtle effects are likely to be important over the next century like changes in silicate supply or turbulence that can influence the relative success of diatoms versus dinoflagellates, coccolithophorids and diazotrophs. In general, inferences drawn from the paleo-oceanographic record and theoretical work suggest that global warming will tend to favor the latter because it will give rise to increased stratification. However, decreases in pH and Fe supply could adversely impact coccolithophorids and diazotrophs in the future. It may be necessary to include explicit dynamic representations of nitrogen fixation, denitrification, silicification and calcification in our models if our goal is predicting the oceanic carbon cycle in the future, because these processes appear to play a very significant role in the carbon cycle of the present-day ocean and they are sensitive to climate change. Observations and models suggest that it may also be necessary to include the DMS cycle to predict future climate, though the effects are still highly uncertain. We have learned a tremendous amount about the distributions and biogeochemical impact of bacteria in the ocean in recent years, yet this improved understanding has not yet been incorporated into many of our models. All of these considerations lead us toward the development of increasingly complex models. However, recent quantitative model intercomparison studies suggest that continuing to add complexity and more functional groups to our ecosystem models may lead to decreases in predictive ability if the models are not properly constrained with available data. We also caution that capturing the present-day variability tells us little about how well a particular model can predict the future. If our goal is to develop models that can be used to predict how the oceans will respond to global warming, then we need to make more rigorous assessments of predictive skill using the available data.

Beschreibung: We review data on the absorption of anthropogenic CO2 by Northern Hemisphere marginal seas (Arctic Ocean, Mediterranean Sea, Sea of Okhotsk, and East/Japan Sea) and its transport to adjacent major basins, and consider the susceptibility to recent climatic change of key factors that influence CO2 uptake by these marginal seas. Dynamic overturning circulation is a common feature of these seas, and this effectively absorbs anthropogenic CO2 and transports it from the surface to the interior of the basins. Amongst these seas only the East/Japan Sea has no outflow of intermediate and deep water (containing anthropogenic CO2) to an adjacent major basin; the others are known to be significant sources of intermediate and deep water to the open ocean. Consequently, only the East/Japan Sea retains all the anthropogenic CO2 absorbed during the anthropocene. Investigations of the properties of the water column in these seas have revealed a consistent trend of waning water column ventilation over time, probably because of changes in local atmospheric forcing. This weakening ventilation has resulted in a decrease in transport of anthropogenic CO2 from the surface to the interior of the basins, and to the adjacent open ocean. Ongoing measurements of anthropogenic CO2, other gases and hydrographic parameters in these key marginal seas will provide information on changes in global oceanic CO2 uptake associated with the predicted increasing atmospheric CO2 and future global climate change. We also review the roles of other marginal seas with no active overturning circulation systems in absorbing and storing anthropogenic CO2. The absence of overturning circulation enables anthropogenic CO2 to penetrate only into shallow depths, resulting in less accumulation of anthropogenic CO2 in these basins. As a consequence of their proximity to populated continents, these marginal seas are particularly vulnerable to human-induced perturbations. Maintaining observation programs will make it possible to assess the effects of human-induced changes on the capacity of these seas to uptake and store anthropogenic CO2.

Beschreibung: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S02, doi:10.1029/2003JC002256.

Beschreibung: GasEx-2001, a 15-day air-sea carbon dioxide (CO2) exchange study conducted in the equatorial Pacific, used a combination of ships, buoys, and drifters equipped with ocean and atmospheric sensors to assess variability and surface mechanisms controlling air-sea CO2 fluxes. Direct covariance and profile method air-sea CO2 fluxes were measured together with the surface ocean and marine boundary layer processes. The study took place in February 2001 near 125°W, 3°S in a region of high CO2. The diurnal variation in the air-sea CO2 difference was 2.5%, driven predominantly by temperature effects on surface solubility. The wind speed was 6.0 ± 1.3 m s−1, and the atmospheric boundary layer was unstable with conditions over the range −1 〈 z/L 〈 0. Diurnal heat fluxes generated daytime surface ocean stratification and subsequent large nighttime buoyancy fluxes. The average CO2 flux from the ocean to the atmosphere was determined to be 3.9 mol m−2 yr−1, with nighttime CO2 fluxes increasing by 40% over daytime values because of a strong nighttime increase in (vertical) convective velocities. The 15 days of air-sea flux measurements taken during GasEx-2001 demonstrate some of the systematic environmental trends of the eastern equatorial Pacific Ocean. The fact that other physical processes, in addition to wind, were observed to control the rate of CO2 transfer from the ocean to the atmosphere indicates that these processes need to be taken into account in local and global biogeochemical models. These local processes can vary on regional and global scales. The GasEx-2001 results show a weak wind dependence but a strong variability in processes governed by the diurnal heating cycle. This implies that any changes in the incident radiation, including atmospheric cloud dynamics, phytoplankton biomass, and surface ocean stratification may have significant feedbacks on the amount and variability of air-sea gas exchange. This is in sharp contrast with previous field studies of air-sea gas exchange, which showed that wind was the dominating forcing function. The results suggest that gas transfer parameterizations that rely solely on wind will be insufficient for regions with low to intermediate winds and strong insolation.

Beschreibung: This work was performed with the support of the National Science Foundation Grant OCE-9986724 and the NOAA Global Carbon Cycle Program Grants NA06GP048, NA17RJ1223, and NA87RJ0445 in the Office of Global Programs.

Beschreibung: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 25 (2011): GB3022, doi:10.1029/2010GB003892.

Beschreibung: The North Atlantic Ocean accounts for about 25% of the global oceanic anthropogenic carbon sink. This basin experiences significant interannual variability primarily driven by the North Atlantic Oscillation (NAO). A suite of biogeochemical model simulations is used to analyze the impact of interannual variability on the uptake and storage of contemporary and anthropogenic carbon (Canthro) in the North Atlantic Ocean. Greater winter mixing during positive NAO years results in increased mode water formation and subsequent increases in subtropical and subpolar Canthro inventories. Our analysis suggests that changes in mode water Canthro inventories are primarily due to changes in water mass volumes driven by variations in water mass transformation rates rather than local air-sea CO2 exchange. This suggests that a significant portion of anthropogenic carbon found in the ocean interior may be derived from surface waters advected into water formation regions rather than from local gas exchange. Therefore, changes in climate modes, such as the NAO, may alter the residence time of anthropogenic carbon in the ocean by altering the rate of water mass transformation. In addition, interannual variability in Canthro storage increases the difficulty of Canthro detection and attribution through hydrographic observations, which are limited by sparse sampling of subsurface waters in time and space.

Beschreibung: We would like to acknowledge funding from the NOAA Climate Program under the Office of Climate Observations and Global Carbon Cycle Program (NOAA‐NA07OAR4310098), NSF (OCE‐0623034), NCAR, the WHOI Ocean Climate Institute, a National Defense Science and Engineering Graduate Fellowship and an Environmental Protection Agency STAR graduate fellowship. NCAR is sponsored by the National Science Foundation.

Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 74 (2013): 48-63, doi:10.1016/j.dsr.2012.12.005.

Beschreibung: Detection and attribution of hydrographic and biogeochemical changes in the deep ocean are challenging due to the small magnitude of their signals and to limitations in the accuracy of available data. However, there are indications that anthropogenic and climate change signals are starting to manifest at depth. The deep ocean below 2000 m comprises about 50% of the total ocean volume, and changes in the deep ocean should be followed over time to accurately assess the partitioning of anthropogenic carbon dioxide (CO2) between the ocean, terrestrial biosphere, and atmosphere. Here we determine the changes in the interior deep-water inorganic carbon content by a novel means that uses the partial pressure of CO2 measured at 20 °C, pCO2(20), along three meridional transects in the Atlantic and Pacific oceans. These changes are measured on decadal time scales using observations from the World Ocean Circulation Experiment (WOCE)/World Hydrographic Program (WHP) of the 1980s and 1990s and the CLIVAR/CO2 Repeat Hydrography Program of the past decade. The pCO2(20) values show a consistent increase in deep water over the time period. Changes in total dissolved inorganic carbon (DIC) content in the deep interior are not significant or consistent, as most of the signal is below the level of analytical uncertainty. Using an approximate relationship between pCO2(20) and DIC change, we infer DIC changes that are at the margin of detectability. However, when integrated on the basin scale, the increases range from 8–40% of the total specific water column changes over the past several decades. Patterns in chlorofluorocarbons (CFCs), along with output from an ocean model, suggest that the changes in pCO2(20) and DIC are of anthropogenic origin.

Beschreibung: Rik Wanninkhof, Geun-Ha Park, John L. Bullister, and Richard A. Feely appreciate the support from the NOAA Office of Atmospheric and Oceanic Research and the Climate Observation Division. S.C.D. acknowledges support from NOAA Grant NA07OAR4310098. T.T. has been supported by grants from NSF and NOAA.

Beschreibung: Author Posting. © Oceanography Society, 2009. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 22 no. 4 (2009): 16-25.

Beschreibung: Over a period of less than a decade, ocean acidification—the change in seawater chemistry due to rising atmospheric carbon dioxide (CO2) levels and subsequent impacts on marine life—has become one of the most critical and pressing issues facing the ocean research community and marine resource managers alike. The objective of this special issue of Oceanography is to provide an overview of the current scientific understanding of ocean acidification as well as to indicate the substantial gaps in our present knowledge. Papers in the special issue discuss the past, current, and future trends in seawater chemistry; highlight potential vulnerabilities to marine species, ecosystems, and marine resources to elevated CO2; and outline a roadmap toward future research directions. In this introductory article, we present a brief introduction on ocean acidification and some historical context for how it emerged so quickly and recently as a key research topic.

Beschreibung: We thank the National Science Foundation (NSF), National Oceanic and Atmospheric Administration (NOAA), and National Aeronautics and Space Administration (NASA) for research support on ocean acidification. We specifically acknowledge grants supporting the OCB Project Office (NSF OCE-0622984, NSF OCE-0927287, and NASA NNX08AX01G). Richard A. Feely was supported by the NOAA Climate Program under the Office of Climate Observations (Grant No. GC04-314 and the Global Carbon Cycle Program (Grant No. GC05-288).