Alkalinity distribution in the western North Atlantic Ocean margins (original) (raw)
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Marine Chemistry, 2014
Climatological mean monthly distributions of pH in the total H + scale, total CO 2 concentration (TCO 2), and the degree of CaCO 3 saturation for the global surface ocean waters (excluding coastal areas) are calculated using a data set for pCO 2 , alkalinity and nutrient concentrations in surface waters (depths b50 m), which is built upon the GLODAP, CARINA and LDEO databases. The mutual consistency among these measured parameters is demonstrated using the inorganic carbon chemistry model with the dissociation constants for carbonic acid by Lueker et al. (2000) and for boric acid by Dickson (1990). Linear potential alkalinity-salinity relationships are established for 24 regions of the global ocean. The mean monthly distributions of pH and carbon chemistry parameters for the reference year 2005 are computed using the climatological mean monthly pCO 2 data adjusted to a reference year 2005 and the alkalinity estimated from the potential alkalinity-salinity relationships. The equatorial zone (4°N-4°S) of the Pacific is excluded from the analysis because of the large interannual changes associated with ENSO events. The pH thus calculated ranges from 7.9 to 8.2. Lower values are located in the upwelling regions in the tropical Pacific and in the Arabian and Bering Seas; higher values are found in the subpolar and polar waters during the spring-summer months of intense photosynthetic production. The vast areas of subtropical oceans have seasonally varying pH values ranging from 8.05 during warmer months to 8.15 during colder months. The warm tropical and subtropical waters are supersaturated by a factor of as much as 4.2 with respect to aragonite and 6.3 for calcite, whereas the cold subpolar and polar waters are supersaturated by 1.2 for aragonite and 2.0 for calcite because of the lower pH values resulting from greater TCO 2 concentrations. In the western Arctic Ocean, aragonite undersaturation is observed. The time-series data from the Bermuda (BATS), Hawaii (HOT), Canary (ESTOC) and the Drake Passage show that pH has been declining at a mean rate of about-0.02 pH per decade, and that pCO 2 has been increasing at about 19 μatm per decade tracking the atmospheric pCO 2 increase rate. This suggests that the ocean acidification is caused primarily by the uptake of atmospheric CO 2. The relative importance of the four environmental drivers (temperature, salinity, alkalinity and total CO 2 concentration) controlling the seasonal variability of carbonate chemistry at these sites is quantitatively assessed. The ocean carbon chemistry is governed sensitively by the TA/TCO 2 ratio, and the rate of change in TA is equally important for the future ocean environment as is the TCO 2 in ocean waters increases in the future.
Southern ocean acidification: A tipping point at 450ppm atmospheric CO2
Iop Conference Series: Earth and Environmental Science, 2009
Southern Ocean acidification via anthropogenic CO2 uptake is expected to be detrimental to multiple calcifying plankton species by lowering the concentration of carbonate ion (CO 3 2؊ ) to levels where calcium carbonate (both aragonite and calcite) shells begin to dissolve. Natural seasonal variations in carbonate ion concentrations could either hasten or dampen the future onset of this undersaturation of calcium carbonate. We present a large-scale Southern Ocean observational analysis that examines the seasonal magnitude and variability of CO 3 2؊ and pH. Our analysis shows an intense wintertime minimum in CO 3 2؊ south of the Antarctic Polar Front and when combined with anthropogenic CO2 uptake is likely to induce aragonite undersaturation when atmospheric CO2 levels reach Ϸ450 ppm. Under the IPCC IS92a scenario, Southern Ocean wintertime aragonite undersaturation is projected to occur by the year 2030 and no later than 2038. Some prominent calcifying plankton, in particular the Pteropod species Limacina helicina, have important veliger larval development during winter and will have to experience detrimental carbonate conditions much earlier than previously thought, with possible deleterious flow-on impacts for the wider Southern Ocean marine ecosystem. Our results highlight the critical importance of understanding seasonal carbon dynamics within all calcifying marine ecosystems such as continental shelves and coral reefs, because natural variability may potentially hasten the onset of future ocean acidification.
Tellus B, 2013
In models of the marine carbon system, it is important to correctly represent riverine and aerial inputs of dissolved inorganic carbon (DIC) and alkalinity. We have examined the different processes contributing to this exchange. In terms of DIC, we have divided the fluxes into their internal component, constituting the carbon ultimately derived from the atmosphere, and their external component originating from rocks. We find that the only process contributing to external DIC input is carbonate and fossil carbon weathering and that erosion of organic matter ultimately constitutes a DIC sink. A number of both riverine and aerial inputs affect the alkalinity. Beside carbonate and silicate weathering, we examine processes of pyrite weathering, aerial input of sulphuric acid, and riverine and aerial inputs of various nitrogen species. Using the observation that, in the ocean, the nitrate concentration follows that of phosphate, we assume a steady state in nitrate. This leads to the surprising result that the only processes affecting the alkalinity is riverine input of nitrate, constituting an alkalinity source and input of ammonia, constituting an alkalinity sink. Furthermore, we compare the flux sizes. As expected, carbonate and silicate weathering has the largest effect on alkalinity, though we note that burial of pyrite might be of importance during periods of large-scale anoxia.
VARIATIONS OF ALKALINITY IN THE NORTHEAST ATLANTIC - PhD Thesis
Total alkalinity (TA) is an important parameter in determining the uptake capacity of anthropogenic CO2 by the ocean. So far, oceanic carbon cycle models do not accurately represent TA and its variations. A spectrophotometric method was developed to measure variations of TA during two JGOFS (Joint Global Ocean Flux Study) cruises to the Northeast Atlantic in the early summer of 1990 and 1991 and in Emiliania huxleyi batch cultures. Short-term precision averaged around ± 0.1 %. A discrepancy of <0.5% with coulometric results was observed in Na2CO3 standards. In natural seawater photometric TA was lower than potentiometric and calculated TA (from partial pressure of CO2, total CO2) by about 1 and 2%, respectively. Discrepancies varied with hydrographic and/or biological regime. Possible reasons for methodological shortcomings were considered, but without certified TA standards for different sample types, it was not possible to make an absolute statement about the accuracy of the methods involved. Combining the cruise results, photometric TA ranged by 90 and 20 µeq*kgSW-1 in the surface mixed layer (SML) and at sub-thermocline depths, respectively. Some horizontal variation in the SML was related to salinity, but most of it could be linked to coccolithophorid growth during a bloom in 1991. Associated small-scale changes in TA of up to 40 µeq*kgSW-1 occurred over 40 km. Independent estimates of seasonal net production of particulate inorganic carbon (PlC) and its relation to that of particulate organic carbon (POC) were established. Based on preceding investigations, a seasonal and latitudinal sequence of changes in surface TA was proposed which was corroborated by the photometric results from this study. The culture experiments revealed reductions in photometric TA which were half of those expected from parallel changes in measured PlC and nitrate concentrations. Proposed explanations for this included methodological shortcomings of all three methods and increases in final TA due to algal sulphate uptake and/or organic acid release. As the main conclusion, further targeted intercomparisons of TA methods are needed to identify the causes for errors in various TA methods in samples covering realistic hydrographic and biological ranges.
1996
An empirical modelling tha! allows il prediction the amount of atmospheric cal consumed by contI nental l'rosion is combined with il river-routing file in order to delermine the spatial distribution of river carbon inputs 10 the world's oceans. The total fluvial carbon input is calculated to be 710 tl'ril gfami of carbon per year (TgC/yr). 205 TgClyr are discharged as dissolved organie carbon, 185 TgClyr ilS particulate organie carbon, and 320 TgC/yr as bicarbonate ions. Of the latter figure, 230 TgOyr stem nom the atmosphere, while the remainder 90 TgC/yr originale trom carbonat? minerai dissolu tion. The Atlantic Ocean receives the grE'atest amount of river carbon, followed by the Pacifie Ocean, the Indian Ocean, and the Aretie Ocean. The "Spatial distribution of the predieted river carbon inputs ma)' be induded in further modelHng rtudies in order 10 better understand the lateral transports of carbon in the pr�nt-day global carbon cyc:le.
Calcium carbonate budget in the Atlantic Ocean based on water column inorganic carbon chemistry
1] Recent independent lines of evidence suggest that the dissolution of calcium carbonate (CaCO 3 ) particles is substantial in the upper ocean above the calcite 100% saturation horizon. This shallow-water dissolution of carbonate particles is in contrast with the current paradigm of the conservative nature of pelagic CaCO 3 at shallow water depths. Here we use more than 20,000 sets of carbon measurements in conjunction with CFC and 14 C data from the WOCE/JGOFS/OACES global CO 2 survey to estimate in situ dissolution rates of CaCO 3 in the Atlantic Ocean. A dissolution rate is estimated from changes in alkalinity as a parcel of water ages along an isopycnal surface. The in situ CaCO 3 dissolution increases rapidly at the aragonite 100% saturation horizon. Estimated dissolution rates north of 40 o N are generally higher than the rates to the south, which is partly attributable to the production of exported CaCO 3 being higher in the North Atlantic than in the South Atlantic. As more CaCO 3 particles move down the water column, more particles are available for in situ dissolution. The total water column CaCO 3 dissolution rate in the Atlantic Ocean is determined on an annual basis by integrating estimated dissolution rates throughout the entire water column and correcting for alkalinity input of approximately 5.6 Â 10 12 mol C yr À1 from CaCO 3 -rich sediments. The resulting water column dissolution rate of CaCO 3 for the Atlantic Ocean is approximately 11.1 Â 10 12 mol C yr À1 . This corresponds to about 31% of a recent estimate (35.8 Â 10 12 mol C yr À1 ) of net CaCO 3 production by for the same area. Our calculation using a large amount of high-quality water column alkalinity data provides the first basin-scale estimate of the CaCO 3 budget for the Atlantic Ocean.
Controls on surface water carbonate chemistry along North American ocean margins
Nature Communications
Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO2 (pCO2) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions ...
Ocean Carbon and Biogeochemistry
In October 2013, the Hawaii Ocean Time-series (HOT) program celebrated its 25 th anniversary. Through sustained support from the U.S. National Science Foundation (NSF), HOT has become one of the longest running, U.S.-led ocean time-series programs in the world. Over the past quarter century, HOT has maintained near-monthly shipboard and laboratory measurements to quantify the biogeochemical and hydrographic state of the North Pacific Subtropical Gyre (NPSG). The primary study site for HOT, Station ALOHA (A Long-term Oligotrophic Habitat Assessment, 21°45´N, 158°W), now serves as a vibrant outpost for numerous research projects. The resulting HOT measurements provide insight into the time-varying interactions among ocean-climate, elemental cycling, and plankton ecology across seasonal to subdecadal scales. Moreover, the long-term record on time-varying change in the ocean's carbonate system documents progressive decreases in seawater pH and steady increases in the partial pressure of CO 2 (pCO 2). In this article, we describe a few of the many contributions of HOT science to our understanding of ocean variability, highlighting some of the people that have devoted a major fraction of their lives over the past quarter century to the program.