1,496 research outputs found
Interannual variability of oceanic CO2 and biogeochemical properties in the Western North Atlantic subtropical gyre
No full textUnderstanding the relationship between Earth's climate and the oceanic carbon cycle requires an understanding of the time-variations of CO2 in the ocean, it's exchange with the atmosphere, and the rate of uptake of anthropogenic CO2 by the ocean. Since 1988, hydrographic and biogeochemical data have been collected at the Bermuda Atlantic Time-Series Study (BATS) site in the Sargasso Sea, located in the North Atlantic subtropical gyre. With over a decade of oceanographic data, interannual trends of CO2 species and air–sea exchange of CO2 at BATS can be examined. Between 1988 and 1998, surface seawater total carbon dioxide (TCO2) and salinity normalized TCO2 (nTCO2) increased at a rate of 2.2±6.9 and 1.6±5.8 ?mol kg?1 yr?1, respectively. During the same period, the partial pressure of CO2 (pCO2) of seawater increased at a rate of 1.4±10.7 ?atm yr?1, similar to the rate of increase in atmospheric pCO2 (?1.3 ?atm yr?1). The increase in seawater TCO2 and pCO2 can be attributed to a combination of uptake of anthropogenic CO2 from the atmosphere and interannual changes in hydrographic properties of the subtropical gyre. Underlying interannual trends were examined by determining how hydrographic and biogeochemical anomalies, or deviations from the mean state, vary over time. Significant correlations existed between anomalies of temperature, salinity, integrated primary production, mixed-layer depth, TCO2, salinity normalized TCO2 (nTCO2), and alkalinity. For example, cold temperature anomalies (up to ?0.5°C) in 1992 and 1995 were associated with increased mixed-layer depth, higher rates of integrated primary production (<?100 mg C m2 d?1), and higher concentrations of nTCO2 (<?5 ?mol kg?1). The interannual anomalies of hydrography and ocean biogeochemistry were partially linked to large-scale climate variability such as North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO). Temperature, mixed-layer depth, primary production and TCO2 anomalies were correlated with NAO variability, with cold anomalies at BATS generally coinciding with NAO negative states. Salinity, alkalinity and nTCO2 anomalies were correlated with the Southern oscillation index (SOI), lagging ENSO events by 6–12 months
Interannual variability of the oceanic CO2sink in the subtropical gyre of the North Atlantic Ocean over the last 2 decades
No full textBetween 1983 and 2005, continuous oceanic CO2 observations at two time series sites in the North Atlantic Ocean near Bermuda indicate that surface seawater dissolved inorganic carbon (DIC) and pCO2 increased annually at rates similar to that expected from oceanic equilibration with increasing CO2 in the atmosphere. In addition, seawater pH, CO32? ion concentrations, and CaCO3 saturation states have also decreased over time. There was considerable seasonal asymmetry in the oceanic CO2 sink or source rates, with wintertime air-to-sea CO2 influx greater than the summertime sea-to-air CO2 efflux. On an annual basis, the region was an oceanic sink for CO2, with a mean net annual air-sea CO2 flux rate of ?815 ± 251 and ?1295 ± 294 mmol CO2 m?2 yr?1, respectively, estimated using different synoptic and data assimilation model wind speed data sets. Peak-to-peak variability of ?850–1950 mmol CO2 m?2 yr?1 represented an interannual variability of ?0.2–0.3 Pg C yr?1 in the oceanic CO2 sink scaled to the subtropical gyre of North Atlantic Ocean. The long-term trend over the 1983–2005 period was a slight increase in the oceanic CO2 sink, associated primarily with a gradual increase in wind speed over the same period. Interannual variability of summertime (June–September) and fall (October–December) air-sea CO2 flux rates were correlated to the North Atlantic Oscillation (NAO) and strongly influenced by wind events such as hurricanes. Wintertime (January–May) air-sea CO2 flux rates were poorly correlated with the NAO and Arctic Oscillation (AO), although gas exchange rates were ?11–40% higher during concurrent El Niño periods compared to La Niña periods
Seasonal variability of the effect of coral reefs on seawater CO2 and air-sea CO2 exchange
No full textThere are complex physical and biological processes controlling the exchange of carbon dioxide (CO2) between the ocean and atmosphere. In coral reef ecosystems, the balance of biological processes such as calcium carbonate (CaCO3) formation and organic carbon production can either lead to CO2 being retained in the oceanic environment (i.e., oceanic sink of CO2) or returned to the atmosphere through gas exchange (oceanic source of CO2). What remains uncertain is the fate of CO2 in reefs subject to seasonal change and the annual balance of air-sea CO2 flux in such systems. Here it is shown that the Bermuda coral reef acts as a sourc of CO2 to seawater overlying the reef. The magnitude of this source of CO2 varies seasonally in response to changes in the reef community between coral- and macroalga-dominated states, reflecting changes in the net balance between calcification and organic carbon production. With knowledge of the calcification rate (~5.6 to 10.6 g CaCO3 m-2 d-1) and observed modification in seawater fCO2 by reef metabolism, rates (20.6 to 3.3 g C m-2 d-1) and seasonal patterns of macroalgal productivity were estimated. Whether the Bermuda coral reef system acts as an oceanic sink or source of CO2 to the atmosphere not only depends on this seasonal variation, but, more importantly, depends on the pre-existing air-sea CO2 disequilibrium of open ocean waters surrounding the reef system. The Bermuda coral reef system serves as a useful model for understanding the fate of CO2 in other reefs, particularly those reefs changing because of environmental stress
Interannual variability in the global uptake of CO2
No full textA major uncertainty are the causes for interannual variability of the global ocean uptake of CO2. Existing estimates, based on atmospheric CO2 data, indicate that peak-to-peak interannual variability in ocean uptake of CO2 is up to 2–4 Pg C year?1 (Pg = 1015 g), while those estimates based on ocean observations and models suggest that year-to-year variability is much smaller (?0.4–0.8 Pg C year?1). Here, it is shown that these differences can be partly reconciled if global air-sea CO2 flux estimates include the CO2 flux associated with tropical cyclones (TC), extra-tropical cyclones (ETC), and new air-sea CO2 gas exchange relationships. The impact of storm events on air-sea CO2 flux is influenced by climate variability such as the El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), contributing to an interannual peak-to-peak variability in global ocean uptake of CO2 of up to ?1.8 Pg C year?1
Twenty years of marine carbon cycle observations at Devils Hole Bermuda provide insights into seasonal hypoxia, coral reef calcification, and ocean acidification
No full textOpen–ocean observations have revealed gradual changes in seawater carbon dioxide (CO2) chemistry resulting from uptake of atmospheric CO2 and ocean acidification (OA), but, with few long–term records (>5 years) of the coastal ocean that can reveal the pace and direction of environmental change. In this paper, observations collected from 1996 to 2016 at Harrington Sound, Bermuda, constitute one of the longest time–series of coastal ocean inorganic carbon chemistry. Uniquely, such changes can be placed into the context of contemporaneous offshore changes observed at the nearby Bermuda Atlantic Time-series Study (BATS) site. Onshore, surface dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2; >10% change per decade) have increased and OA indicators such as pH and calcium carbonate (CaCO3) saturation state (Ω) decreased from 1996 to 2016 at a rate of two to three times that observed offshore at BATS. Such changes, combined with reduction of total alkalinity over time, reveal a complex interplay of biogeochemical processes influencing Bermuda reef metabolism, including net ecosystem production (NEP = gross primary production–autotrophic and heterotrophic respiration) and net ecosystem calcification (NEC = gross calcification–gross CaCO3 dissolution). These long–term data show a seasonal shift between wintertime net heterotrophy and summertime net autotrophy for the entire Bermuda reef system. Over annual time-scales, the Bermuda reef system does not appear to be in trophic balance, but rather slightly net heterotrophic. In addition, the reef system is net accretive (i.e., gross calcification > gross CaCO3 dissolution), but there were occasional periods when the entire reef system appears to transiently shift to net dissolution. A previous 5–year study of the Bermuda reef suggested that net calcification and net heterotrophy have both increased. Over the past 20 years, rates of net calcification and net heterotrophy determined for the Bermuda reef system have increased by ~30%, most likely due to increased coral nutrition occurring in concert with increased offshore productivity in the surrounding subtropical North Atlantic Ocean. Importantly, this long–term study reveals that other environmental factors (such as coral feeding) can mitigate against the effects of ocean acidification on coral reef calcification, at least over the past couple of decades
Investigation of the Physical and Biological Controls of the Oceanic CO2 System in the Sargasso Sea
No full textAir-sea CO<sub>2</sub> fluxes and the continental shelf pump of carbon in the Chukchi Sea adjacent to the Arctic Ocean
No full textThe Chukchi Sea, a shallow sea-ice covered coastal sea adjacent to the Arctic Ocean, exhibits an intense bloom of phytoplankton each year due to the exposure of nutrient-laden surface waters during the brief summertime retreat and melting of sea-ice. The impact of phytoplankton production and other factors on the seasonal dynamics of carbon and air-sea CO2 fluxes were investigated during two survey cruises (5 May–15 June 2002, and 17 July–26 August 2002), as part of the Western Arctic Shelf-Basins-Interactions (SBI) project. In springtime, most of the Chukchi Sea was sea-ice covered (>95%) and remnant winter water was present across the shelf. Surface layer seawater partial pressure of CO2 (pCO2) ranged from ~200–320 µatm, indicative of undersaturation with respect to atmospheric pCO2, although sea-ice cover kept rates of air-to-sea CO2 flux generally low (<1 mmoles CO2 m2 d-1). By summertime, after sea-ice retreat, seawater pCO2 contents had decreased to very low values (<80–220 µatm) in response to high rates of localized primary and net community production (NCP) and biological uptake of dissolved inorganic carbon (DIC). In the seasonally sea-ice free regions of the Chukchi Sea shelf, rates of air-to-sea CO2 fluxes, determined using the quadratic wind speed-transfer velocity relationships of Wanninkhof (1992), were high, ranging from ~30–90 mmoles CO2 m-2 d-1. In regions of the Chukchi Sea slope (and western Beaufort Sea shelf and Arctic Ocean basin) where sea-ice cover remained high (>80%), air-to-sea CO2 fluxes remained generally low (<2 mmoles CO2 m-2 d-1). Seasonal (i.e., May to September) and annual net air-to-sea CO2 fluxes from the Chukchi Sea shelf were estimated at ~27 ± 7 Tg C yr-1, and 38 ± 7 Tg C yr-1, respectively. The Chukchi Sea represents the largest oceanic CO2 sink in the marginal coastal seas adjacent to the Arctic Ocean. An active continental shelf pump of carbon, driven by the northward transport of nutrient-rich water of Pacific Ocean origin, high rates of primary and net community production during the sea-ice free period, and lateral export of organic carbon, maintains the Chukchi Sea shelf and slope as a perennial ocean CO2 sink
Assessing Ocean Acidification Variability in the Pacific-Arctic Region as Part of the Russian-American Long-term Census of the Arctic
No full textThe Russian-American Long-term Census of the Arctic (RUSALCA) project provides a rare opportunity to study the Russian sector of the Pacific Arctic Region (PAR), which includes the Chukchi and East Siberian Seas. RUSALCA data from 2009 and 2012 allow fuller understanding of changes in ocean chemistry across this the region and, in particular, provide perspectives on the ocean carbon cycle, air-sea CO2 gas exchange, and ocean acidification variability. Summertime surface waters of the western Chukchi Sea and East Siberian Sea mostly exhibited low pCO2 (<100 to 400 µatm) and high pH (8.0 to 8.4) conditions during sea ice retreat. As earlier studies of the adjacent eastern Chukchi Sea show, this area of the PAR had a strong potential for ocean uptake of atmospheric CO2 , with saturation states for calcium carbonate (CaCO3) minerals such as calcite and aragonite (?calcite and ?aragonite, respectively) having values generally greater than two, thereby facilitating CaCO3 production. In contrast, fresher surface waters flowing into the Chukchi Sea from the East Siberian Sea and bottom waters on the PAR shelves exhibited high pCO2 and low pH, ?calcite, and ?aragonite conditions. Low ? surface waters near the Russian coast and nearly 70% of waters next to the seafloor were corrosive to CaCO3 minerals such as aragonite, with this change seemingly occurring at a more rapid rate than typical global open-ocean changes in ocean chemistry. The exposure of subsurface benthic communities and nearshore ecosystems near the Russian coast to potentially corrosive water is likely exacerbated by the ocean uptake of anthropogenic CO2 and gradual ocean acidification. The RUSALCA project also highlights the complexities and uncertainties in the physical and biogeochemical drivers of the ocean carbon cycle and ocean chemistry in this region of the Arctic
Discussion: Early Devonian marine isotopic signatures: brachiopods from the Upper Gaspé limestones, Gaspé Peninsula, Québec, Canada
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