1,721,114 research outputs found
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
Full text linkThe 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
No full textThe influence of short-term wind variability on air-sea CO2 exchange
No full textQuantifying the regional and global exchange of CO2 between the ocean and atmosphere requires knowledge of the factors that affect CO2 gas transfer (e.g., wind speed) and the air-sea difference in partial pressure of CO2 (pCO2). A major uncertainty is the effect of short-term variability on air-sea CO2 flux. Using high sampling frequency wind speed and pCO2 data collected during deployments of the autonomous CARbon Interface OCean Atmosphere (CARIOCA) buoy, we compare CO2 fluxes at different sampling frequency of wind speed (i.e., hourly versus daily averaged). Air-sea CO2 flux was up to three times greater if high frequency wind data was used rather than daily average values. This difference arises from the non-linear relationship between wind speed and CO2 gas transfer coefficient, and a better representation of wind distribution at a higher frequency (i.e., hourly) of sampling. This finding has significant implications for determining regional and global air-sea CO2 fluxes, and understanding of the global carbon cycle
Secular variation of calcium carbonate mineralogy; an evaluation of ooid and micrite chemistries
No full textThree ooid types are recognized from the Lower Tournaisian »Kohlenkalk« shelf facies at Velbert, Germany. Ooids from this unit have a predominantly concentric laminae fabric. Radial-concentric and small radial fibrous ooids are minor components to this oolite. The diagenetic response of Kohlenkalk ooid chemistry is significantly different from that observed in contemporaneous crinoid and brachiopod material. Fabric evidence suggests that radial-concentric and radial-fibrous ooids were probably originally aragonite/high-Mg calcite and high-Mg calcite respectively. Fabric and trace elemental chemistries of the concentric fabric ooids suggests that they were originally precipitated as aragonite and subsequently altered to low-Mg calcite.Recent papers have proposed temporal shifts in the dominant mineralogy of shallow marine non-skeletal carbonates between calcite and aragonite. Changing Phanerozoic atmospheric pCO2 levels and oceanic Mg/Ca ratios may have been factors controlling the dominant mineralogy. The chemistries of the Kohlenkalk ooids in conjunction with other ooid and micrite data spanning the Mid-Paleozoic to Recent are evaluated in context with these temporal shifts between »calcite« and »aragonite seas«. The strontium chemistries of the ooids (¯x = 1010 ppm, range 145–3010 ppm) and micrites (¯x = 841 ppm, range 3–8800 ppm) suggests they had an aragonite precursor mineralogy. No statistical correlation was observed between ooid/micrite chemistries, their mineralogies and the proposed secular trend. Therefore, we suggest that aragonitic ooids and micrites were dominant components of shallow-marine carbonate environments throughout the Phanerozoic. The distribution and abundance of aragonitic and calcitic ooids in the geologic past was probably dependant on local hydraulic, physicochemical, and environmental conditions, areally constrained by global tectonics, eustatic, climatic and atmospheric effects, with significant diagenetic overprinting of the original geochemical and fabric information.<br/
Environmental and physiological influences on isotopic and elemental compositions of brachiopod shell calcite: Implications for the isotopic evolution of Paleozoic oceans
No full textBrachiopods from the Demissa Bed (Middle Devonian, Hamilton Group) biologically regulated the incorporation of Mg, Sr and Na into their shell calcite. Significant taxonomic differences in the elemental contents of three species (Athyris spiriferoides, Mediospirifer audacula and Mucrospirifer mucronatus) may be related to differences in calcification processes. In contrast, no significant difference or “vital effects” were observed between the isotopic values of Mediospirifer audacula and Athyris spiriferoides from Erie (?18O=0.03‰, p=0.949; ?13C=0.76‰, p=0.083) and Genessee Counties (?18O=0.39‰, p=0.471; ?13C=0.06‰, p=0.854). This suggests that these brachiopods did not exert a biological control over their isotopic compositions, and that their shell calcites reflect ambient physicochemical conditions.Isotopic compositions in unaltered shell calcites of brachiopods from Genessee County, which was close to the basin depocentre, are heavy for carbon (?13C, View the MathML source=+5.01‰, PDB) and oxygen (?18C, View the MathML source=?2.85‰, PDB) compared to the species sampled at the basin's edge (Erie County; (?13C, View the MathML source=+2.79‰, PDB; ?18O, View the MathML source=?3.83‰, PDB). There is a significant separation in isotopic values between the deeper- and shallower-water brachiopods of the basin ((?18O=0.98‰, p=0.0005; ?13C=2.22‰, p=0.0005). The ?18O variation suggests a temperature/salinity change with water depth, whereas the change in ?13C composition probably records an enrichment /depletion of organic matter with water depth. This observation has significant implications for Paleozoic ocean isotopic-evolution studies, because many global changes in marine ?18O and ?13C are based on isotopic shifts of similar magnitude
- …
