Air-sea CO2 Research Articles

Air-sea CO2fluxes above the stratified oxygen minimum zone in the coastal region off Mexico

Oxygen minimum zones (OMZs) are important sources of CO2 to the atmosphere when physical forces bring subsurface water with high dissolved inorganic carbon (DIC) to the surface. This study examines, for the first time, the influence of the OMZ of the coastal North Eastern Tropical Pacific off Mexico on surface CO2 fluxes. We use variations in the oxycline depth and subsurface water masses to discern physical oceanographic influences. During two cruises, in November 2009 and August 2010, DIC and total alkalinity (TA) measurements were used to estimate pCO2 and air-sea CO2 fluxes. At the OMZ layer, Subtropical Subsurface Water (StSsW) was found to have high pCO2 values (1290 ± 70 μatm). Due to strong vertical stratification, however, the relationship between ΔpCO2 at the air-sea interface and the oxycline/StSsW upper limit depth was weak. During November, the region was a weak source of CO2 to the atmosphere (up to 2.5 mmol C m−2 d−1), while during August a range of values were observed between −4.4 and 3.3 mmol C m−2 d−1). Strong stratification (>1200 J m−3) prevented subsurface mixing of water from the OMZ to the upper layer; particularly in November 2009 which was during an El Niño event. Results suggest that advection of surface water masses, reinforced by strong vertical stratification, controlled surface pCO2, and air-sea CO2 fluxes.

海洋生态系统固碳能力估算方法研究进展

The control of greenhouse gas is arguably the most challenging environmental policy issue facing China and other countries. CO 2 is considered to be the major greenhouse gas( GHG) contributing to global warming. Ocean is the largest active carbon pool,and plays an important role in globe climate change. And it is of great significance in the global carbon cycle to accurately estimate the absorbance,transformation,deposition rate of the carbon element in the marine ecosystem. In general,the air-sea CO 2 exchange fluxes were estimated from CO 2 partial pressure between the atmosphere and surface seawater,the primary productivity of phytoplankton was calculated by use of the biogeochemical models based on chlorophyll concentrations in the sea,particle organic carbon( POC) export fluxes in the euphotic zone were derived with 234Th—238U disequilibrium in the upper water column,and the organic carbon deposition rate was measured from210Pb specific activity vertical distribution in the sediment,respectively. Improvements in knowledge of the magnitude of this oceanic carbon uptake can be made thanks to an emerging international observation network that allow routine monitoring of the oceanic CO 2 uptake,on decadal and basin scales. However,not all uncertainties have been resolved,and the high variability of oceanic environments means that a unified description of marine carbon sequestration cannot yet be achieved. For example,there is no invaluable information to illustrate the mutual influence on carbon exchange flux in different medium of the atmosphere,sea water,and sedimentation,respectively,although the amount of carbon sequestration had been investigated in the single medium. There is unclear knowledge to indicate the key factors controlling carbon cycle process in the whole system,which includes the air-sea CO 2 exchange,the primary productivity of phytoplankton in the sea, POC export in the euphotic zone,and the organic carbon deposition in the sediment. It would be extremely challenging to quantify with acceptable accuracy the carbon sequestration in the ocean on a long term basis,and to adequately monitor unintended impacts over large space and time-scales. So,meaningful projections of future behavior of the oceanic sink are more challenging. Attempts to set a baseline stabilization target for the atmospheric CO 2 concentration will ultimately depend on an improved understanding of the oceanic mechanism regulating CO 2 uptake and the ability to make useful predictions of this parameter. To further improve the carbon sequestration assessment method in marine ecosystem,the comprehensive knowledge is required to form the assessment system that consists of the observation techniques,analysis method and the amount of carbon sequestration estimate. Furthermore,the index,criterion and standard,as well as evaluating the standard system of carbon sequestration in the marine ecosystem should be addressed in order to meet the demand of carbon reduction and carbon sink increase in China.

Distribution of total alkalinity and pH in the Ross Sea (Antarctica) waters during austral summer 2008

Measurements of total alkalinity (A T ) and pH were made in the Ross Sea in January–February 2008 in order to characterize the carbonate system in the Ross Sea and to evaluate the variability associated with different water masses. The main water masses of the Ross Sea, Antarctic Surface Water, High Salinity Shelf Water (HSSW), Deep Ice Shelf Water, Circumpolar Deep Water (CDW) and Antarctic Bottom Water, were identified on the basis of the physical and chemical data. In particular, the A T ranged between 2275 and 2374 µmol kg −1 with the lowest values in the surface waters (2275–2346 µmol kg −1 ), where the influence of the sea-ice melting and of the variability of the physical properties was significant. In the deep layers of the water column, the A T maxima were measured in correspondence to the preferential pathways of the spreading HSSW. The pH had variable values in the surface layer (7.890–8.033) with the highest values in Terra Nova Bay and Ross Sea polynyas. A low pH (7.969±0.025) traced the intrusion of the CDW in the Ross Sea shelf area. All samples revealed waters that were oversaturated with respect to both calcite and aragonite, but near corrosive levels of aragonite saturation state (Ω ca. 1.1–1.2) were associated with the entrainment of CDW over the slope. Aragonite undersaturation is of particular concern for the zooplankton species comprising to calcifying organisms such as pteropods. The partial pressure of CO 2 at the sea surface was undersaturated with respect to the atmospheric value, particularly in Terra Nova Bay and the Ross Sea polynyas, but a large variability in the sea–air CO 2 fluxes was observed associated with different responses in the strength of the biological and physical processes. Keywords: Total alkalinity; pH; saturation state; Terra Nova Bay polynya; Ross Sea (Published: 16 October 2014) Citation: Polar Research 2014, 33 , 20403, http://dx.doi.org/10.3402/polar.v33.20403

Observed trends of <i>p</i>CO<sub>2</sub> and air-sea CO2 fluxes in the North Atlantic Ocean

Observed partial pressure of carbon dioxide ( p CO 2 ) and temperature data in surface and mixed layer seawater of the Northeast (49 o N, 16.5 o W) and Northwest (56.5 o N, 52.6 o W) Atlantic Ocean time series sites have been analyzed for seasonal variability and air-sea CO 2 fluxes. The NE PAP data showed an annual mean p CO 2 of 335.9 ± 89.6 m atm (2003), 286.7 ± 103.5 m atm (2004), and 335.9 ± 89.6 m atm (2005). The annual data for NW KI deployments indicated annual p CO 2 average of 336.6 ± 14.3 and 359.1 ± 25.3 m atm for 2004 and 2005 respectively. The oceanic p CO 2 distribution across the spatial gradients over a seasonal timescale is relatively homogeneous with marked seasonal variability. These data indicated consistently the undersaturation of oceanic surface water at the sites and thus a perennial carbon sink. Sea surface p CO 2 trend is marked by summertime minimum and wintertime maximum, while depicting anti-phase patterns with the observed temperature signals. Seasonal to annual CO 2 fluxes indicated a year-round CO 2 invasion of the NE and NW basins. Estimated net basin-scale CO 2 uptake fluxes of 2.96 ± 1.73 and 1.84 ± 1.3 mol m -2 CO 2 a -1 were obtained for NE PAP (2nd - 4th) and NW K1 deployments, respectively.

Synoptic evaluation of carbon cycling in the Beaufort Sea during summer: contrasting river inputs, ecosystem metabolism and air-sea CO2 fluxes

Synoptic evaluation of carbon cycling in the Beaufort Sea during summer: contrasting river inputs, ecosystem metabolism and air-sea CO<SUB>2</SUB> fluxes

Interannual sea-air CO2 flux variability from an observation-driven ocean mixed-layer scheme

Interannual sea-air CO<SUB>2</SUB> flux variability from an observation-driven ocean mixed-layer scheme

Seasonal variations of sea–air CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes in the largest tropical marginal sea (South China Sea) based on multiple-year underway measurements

Abstract. Based upon 14 field surveys conducted between 2003 and 2008, we showed that the seasonal pattern of sea surface partial pressure of CO2 (pCO2) and sea–air CO2 fluxes differed among four different physical–biogeochemical domains in the South China Sea (SCS) proper. The four domains were located between 7 and 23° N and 110 and 121° E, covering a surface area of 1344 × 103 km2 and accounting for ~ 54% of the SCS proper. In the area off the Pearl River estuary, relatively low pCO2 values of 320 to 390 μatm were observed in all four seasons and both the biological productivity and CO2 uptake were enhanced in summer in the Pearl River plume waters. In the northern SCS slope/basin area, a typical seasonal cycle of relatively high pCO2 in the warm seasons and relatively low pCO2 in the cold seasons was revealed. In the central/southern SCS area, moderately high sea surface pCO2 values of 360 to 425 μatm were observed throughout the year. In the area west of the Luzon Strait, a major exchange pathway between the SCS and the Pacific Ocean, pCO2 was particularly dynamic in winter, when northeast monsoon induced upwelling events and strong outgassing of CO2. These episodic events might have dominated the annual sea–air CO2 flux in this particular area. The estimate of annual sea–air CO2 fluxes showed that most areas of the SCS proper served as weak to moderate sources of the atmospheric CO2, with sea–air CO2 flux values of 0.46 ± 0.43 mol m−2 yr−1 in the northern SCS slope/basin, 1.37 ± 0.55 mol m−2 yr−1 in the central/southern SCS, and 1.21 ± 1.48 mol m−2 yr−1 in the area west of the Luzon Strait. However, the annual sea–air CO2 exchange was nearly in equilibrium (−0.44 ± 0.65 mol m−2 yr−1) in the area off the Pearl River estuary. Overall the four domains contributed (18 ± 10) × 1012 g C yr−1 to the atmospheric CO2.

Sea–air CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes in the Indian Ocean between 1990 and 2009

Abstract. The Indian Ocean (44° S–30° N) plays an important role in the global carbon cycle, yet it remains one of the most poorly sampled ocean regions. Several approaches have been used to estimate net sea–air CO2 fluxes in this region: interpolated observations, ocean biogeochemical models, atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Indian Ocean sea–air CO2 fluxes between 1990 and 2009. Using all of the models and inversions, the median annual mean sea–air CO2 uptake of −0.37 ± 0.06 PgC yr−1 is consistent with the −0.24 ± 0.12 PgC yr−1 calculated from observations. The fluxes from the southern Indian Ocean (18–44° S; −0.43 ± 0.07 PgC yr−1 are similar in magnitude to the annual uptake for the entire Indian Ocean. All models capture the observed pattern of fluxes in the Indian Ocean with the following exceptions: underestimation of upwelling fluxes in the northwestern region (off Oman and Somalia), overestimation in the northeastern region (Bay of Bengal) and underestimation of the CO2 sink in the subtropical convergence zone. These differences were mainly driven by lack of atmospheric CO2 data in atmospheric inversions, and poor simulation of monsoonal currents and freshwater discharge in ocean biogeochemical models. Overall, the models and inversions do capture the phase of the observed seasonality for the entire Indian Ocean but overestimate the magnitude. The predicted sea–air CO2 fluxes by ocean biogeochemical models (OBGMs) respond to seasonal variability with strong phase lags with reference to climatological CO2 flux, whereas the atmospheric inversions predicted an order of magnitude higher seasonal flux than OBGMs. The simulated interannual variability by the OBGMs is weaker than that found by atmospheric inversions. Prediction of such weak interannual variability in CO2 fluxes by atmospheric inversions was mainly caused by a lack of atmospheric data in the Indian Ocean. The OBGM models suggest a small strengthening of the sink over the period 1990–2009 of −0.01 PgC decade−1. This is inconsistent with the observations in the southwestern Indian Ocean that shows the growth rate of oceanic pCO2 was faster than the observed atmospheric CO2 growth, a finding attributed to the trend of the Southern Annular Mode (SAM) during the 1990s.

Modelling ocean acidification in the Nordic and Barents Seas in present and future climate

An ecosystem model, NORWECOM.E2E including a module for the carbonate system, has been used to investigate the effects of rising atmospheric CO2 and climate change on the ocean's acid–base state in the Nordic and Barents Seas. Using the 20C3M control run and the A1B emission scenario, a downscaling of the GISS-AOM global climate model has been used to force the ecosystem model for a reference (1981–2000) and a future climate (2046–2065) simulation respectively. The simulations demonstrate how the saturation state of seawater with respect to aragonite will evolve, with a shoaling of the saturation horizon of approximately 1200m in the Nordic Seas, and a large increase in area extent of under saturated surface waters. The simulated pH change in the surface water is −0.19 from 2000 to 2065, while the model estimates an almost doubling of the CO2 air–sea flux in the Barents Sea increasing the uptake from 23 to 37gCm−2yr−1. The main driver for the modelled changes in surface fCO2 is the change in DIC, with only minor contributions from temperature, salinity and total alkalinity.

Riverine influence on the tropical Atlantic Ocean biogeochemistry

Abstract. We assess the role of riverine inputs of N, Si, Fe, organic and inorganic C in the tropical Atlantic Ocean using a global ocean biogeochemistry model. We use a standard model scenario and three sensitivity tests to investigate the role of total river nutrient and carbon inputs, as well as the western (South American) and eastern (African) river inputs on the tropical Atlantic Ocean biogeochemistry, between 20° S–20° N and 70° W–20° E. Increased nutrient availability from river inputs in this area (compared to a sensitivity scenario without river nutrient inputs, NO_RIVER) leads to an increase in primary production (PP) and export production (EP), mainly in the coastal ocean area (modeled ocean area with bathymetry &lt;200 m). Model results suggest an enhanced N-fixation by diazotrophs on the tropical Atlantic mainly in open ocean areas. The increased rate of N-fixation in the TODAY scenario is proportional to the increase in PP and EP relative to the NO_RIVER scenario, and may support up to 14% of the coastal ocean export production. Inputs from South American rivers have an impact in coastal PP and EP two times higher than those from African rivers. On the other hand, results suggest that the contribution of African and South American rivers to the total increase in open ocean PP and EP is similar. Considering the amount of delivered nutrients (2–3 times less nutrients and carbon inputs by African rivers) one concludes that African riverine inputs may have a larger impact on the whole tropical Atlantic Ocean biogeochemistry. This is probably due to a combination of nutrient trapping in upwelling areas off the large rivers' outflows and shallow mixed layers in the eastern tropical Atlantic, concomitantly to the differences in delivered nutrient ratios leading to alleviation in limitation conditions, mainly for diatoms. When river inputs are added to the model, we estimate a modest decrease in open ocean sea-air CO2 fluxes (−5.2 Tg C a−1) and an increase in coastal ocean CO2 fluxes, mainly provoked by the remineralization of riverine organic matter delivered by the South American rivers.

Air-sea CO2fluxes in the near-shore and intertidal zones influenced by the California Current

[1] The study of air-sea CO2 fluxes (FCO2) in the coastal region is needed to better understand the processes that influence the direction and magnitude of FCO2 and to constrain the global carbon budget. We implemented a 1 year (January through December 2009) paired study to measure FCO2 in the intertidal zone (the coastline to 1.6 km offshore) and the near-shore (∼3 km offshore) off the north-western coast of Baja California (Mexico); a region influenced by year-round upwelling. FCO2 was determined in the intertidal zone via eddy covariance; while in the near-shore using mooring buoy sensors then calculated with the bulk method. The near-shore region was a weak annual net source of CO2 to the atmosphere (0.043 mol CO2 m−2 y−1); where 91% of the outgassed FCO2 was contributed during the upwelling season. Sea surface temperature (SST) and ΔpCO2 (from upwelling) showed the strongest relationship with FCO2 in the near-shore, suggesting the importance of meso-scale processes (upwelling). FCO2 in the intertidal zone were up to four orders of magnitude higher than FCO2 in the near-shore. Wind speed showed the strongest relationship with FCO2 in the intertidal zone, suggesting the relevance of micro-scale processes. Results show that there are substantial spatial and temporal differences in FCO2 between the near-shore and intertidal zone; likely a result of heterogeneity. We suggest that detailed spatial and temporal measurements are needed across the coastal oceans and continental margins to better understand the mechanisms which control FCO2, as well as reduce uncertainties and constrain regional and global ocean carbon balances.

Surface ocean p CO2 seasonality and sea-air CO2 flux estimates for the North American east coast

[1] Underway and in situ observations of surface ocean pCO2, combined with satellite data, were used to develop pCO2 regional algorithms to analyze the seasonal and interannual variability of surface ocean pCO2 and sea-air CO2 flux for five physically and biologically distinct regions of the eastern North American continental shelf: the South Atlantic Bight (SAB), the Mid-Atlantic Bight (MAB), the Gulf of Maine (GoM), Nantucket Shoals and Georges Bank (NS+GB), and the Scotian Shelf (SS). Temperature and dissolved inorganic carbon variability are the most influential factors driving the seasonality of pCO2. Estimates of the sea-air CO2 flux were derived from the available pCO2 data, as well as from the pCO2 reconstructed by the algorithm. Two different gas exchange parameterizations were used. The SS, GB+NS, MAB, and SAB regions are net sinks of atmospheric CO2 while the GoM is a weak source. The estimates vary depending on the use of surface ocean pCO2 from the data or algorithm, as well as with the use of the two different gas exchange parameterizations. Most of the regional estimates are in general agreement with previous studies when the range of uncertainty and interannual variability are taken into account. According to the algorithm, the average annual uptake of atmospheric CO2 by eastern North American continental shelf waters is found to be between −3.4 and −5.4 Tg C yr−1 (areal average of −0.7 to −1.0 mol CO2 m−2 yr−1) over the period 2003–2010.

Photosynthetic carbon fixation by tropical coral reef phytoplankton assemblages: a UVR perspective

Photosynthetic carbon fixation regulates air-sea CO 2 fluxes in the waters of coral reefs. However, little has been docu mented on the effects of solar UV radiation (UVR, 280-400 nm) upon photosynthetic behaviors of phytoplankton dwelling in these ecosystems. In order to evaluate the aforesaid, surface dwelling tropical coral reef phytoplankton assemblages collected from the South China Sea were exposed to solar radiation (i.e., photosynthetically active radiation [PAR] + UV radiation A [UVA] + UV radiation B [UVB], 280-700 nm; PAR + UVA, 320-700 nm; and PAR, 400-700 nm) under static or simulated-mixing conditions. Under the static condition, UVA and UVB significantly reduced the carbon fixation with the maximum of 22.4 and 15.3%, respectively; while lower UVR-related photosynthetic inhibition was observed in case of phytoplankton samples being subjected to mixing. At a moderate level of mixing (i.e., circulation time 80 min), the UVA and UVB caused inhibition were lowered by 52.1 and 79.6%, respectively. Based on this it could be stated that vertical mixing induced by winds and/or tides in the natural environments could reduce the inhibitory effect of solar UVR on phytoplankton productivity in the coral reefs water.

Twentieth-Century Oceanic Carbon Uptake and Storage in CESM1(BGC)*

Abstract Ocean carbon uptake and storage simulated by the Community Earth System Model, version 1–Biogeochemistry [CESM1(BGC)], is described and compared to observations. Fully coupled and ocean-ice configurations are examined; both capture many aspects of the spatial structure and seasonality of surface carbon fields. Nearly ubiquitous negative biases in surface alkalinity result from the prescribed carbonate dissolution profile. The modeled sea–air CO2 fluxes match observationally based estimates over much of the ocean; significant deviations appear in the Southern Ocean. Surface ocean pCO2 is biased high in the subantarctic and low in the sea ice zone. Formation of the water masses dominating anthropogenic CO2 (Cant) uptake in the Southern Hemisphere is weak in the model, leading to significant negative biases in Cant and chlorofluorocarbon (CFC) storage at intermediate depths. Column inventories of Cant appear too high, by contrast, in the North Atlantic. In spite of the positive bias, this marks an improvement over prior versions of the model, which underestimated North Atlantic uptake. The change in behavior is attributable to a new parameterization of density-driven overflows. CESM1(BGC) provides a relatively robust representation of the ocean–carbon cycle response to climate variability. Statistical metrics of modeled interannual variability in sea–air CO2 fluxes compare reasonably well to observationally based estimates. The carbon cycle response to key modes of climate variability is basically similar in the coupled and forced ocean-ice models; however, the two differ in regional detail and in the strength of teleconnections.

Sea-air CO2 fluxes in the Indian Ocean between 1990 and 2009

Sea-air CO₂ fluxes in the Indian Ocean between 1990 and 2009

The Gulf of Alaska coastal ocean as an atmospheric CO2 sink

A new data set of directly measured surface seawater carbon dioxide partial pressures (pCO2) was compiled for the Gulf of Alaska (GOA) coastal ocean. Using this information, along with reconstructed atmospheric pCO2 data, we calculate sea–air CO2 fluxes over two interconnected domains: the coastal ocean defined by the Surface Ocean CO2 Atlas (SOCAT) Continental Margin Mask, and the continental margin shoreward of the 1500m isobath. The continental margin in this region lies within the coastal ocean. Climatological sea–air CO2 fluxes were calculated by constructing monthly climatologies of sea–air pCO2 difference (ΔpCO2), sea surface temperature, salinity, and CO2 solubility, coupled with the monthly second moment of wind speeds from the Scatterometer Climatology of Ocean Winds (SCOW; http://cioss.coas.oregonstate.edu/scow). Climatological sea–air CO2 fluxes showed instances of atmospheric CO2 uptake and outgassing in both domains for nearly all months; however, uptake dominated from April through November, with distinct spring and autumn peaks that coincided with periods of strong winds and undersaturated surface seawater pCO2 with respect to atmospheric levels. Atmospheric CO2 uptake during the spring and autumn peaks was stronger on the continental margin compared with the coastal ocean. Annual mean area-weighted fluxes for the coastal ocean and continental margin were −2.5 and −4mmolCO2m−2d−1, respectively. Scaling these annual means by the respective surface areas of each domain resulted in estimates of substantial atmospheric CO2 uptake between 34 and 14TgCyr−1. This region is a large sink for atmospheric CO2, which impacts the current view of weak net CO2 emission from coastal waters surrounding North America.

Sea–air CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes in the Southern Ocean for the period 1990–2009

Abstract. The Southern Ocean (44–75° S) plays a critical role in the global carbon cycle, yet remains one of the most poorly sampled ocean regions. Different approaches have been used to estimate sea–air CO2 fluxes in this region: synthesis of surface ocean observations, ocean biogeochemical models, and atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Southern Ocean sea–air CO2 fluxes between 1990–2009. Using all models and inversions (26), the integrated median annual sea–air CO2 flux of −0.42 ± 0.07 Pg C yr−1 for the 44–75° S region, is consistent with the −0.27 ± 0.13 Pg C yr−1 calculated using surface observations. The circumpolar region south of 58° S has a small net annual flux (model and inversion median: −0.04 ± 0.07 Pg C yr−1 and observations: +0.04 ± 0.02 Pg C yr−1), with most of the net annual flux located in the 44 to 58° S circumpolar band (model and inversion median: −0.36 ± 0.09 Pg C yr−1 and observations: −0.35 ± 0.09 Pg C yr−1). Seasonally, in the 44–58° S region, the median of 5 ocean biogeochemical models captures the observed sea–air CO2 flux seasonal cycle, while the median of 11 atmospheric inversions shows little seasonal change in the net flux. South of 58° S, neither atmospheric inversions nor ocean biogeochemical models reproduce the phase and amplitude of the observed seasonal sea–air CO2 flux, particularly in the Austral Winter. Importantly, no individual atmospheric inversion or ocean biogeochemical model is capable of reproducing both the observed annual mean uptake and the observed seasonal cycle. This raises concerns about projecting future changes in Southern Ocean CO2 fluxes. The median interannual variability from atmospheric inversions and ocean biogeochemical models is substantial in the Southern Ocean; up to 25% of the annual mean flux, with 25% of this interannual variability attributed to the region south of 58° S. Resolving long-term trends is difficult due to the large interannual variability and short time frame (1990–2009) of this study; this is particularly evident from the large spread in trends from inversions and ocean biogeochemical models. Nevertheless, in the period 1990–2009 ocean biogeochemical models do show increasing oceanic uptake consistent with the expected increase of −0.05 Pg C yr−1 decade−1. In contrast, atmospheric inversions suggest little change in the strength of the CO2 sink broadly consistent with the results of Le Quéré et al. (2007).

Net sea–air CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; flux uncertainties in the Bay of Biscay based on the choice of wind speed products and gas transfer parameterizations

Abstract. The estimation of sea–air CO2 fluxes is largely dependent on wind speed through the gas transfer velocity parameterization. In this paper, we quantify uncertainties in the estimation of the CO2 uptake in the Bay of Biscay resulting from the use of different sources of wind speed such as three different global reanalysis meteorological models (NCEP/NCAR 1, NCEP/DOE 2 and ERA-Interim), one high-resolution regional forecast model (HIRLAM-AEMet), winds derived under the Cross-Calibrated Multi-Platform (CCMP) project, and QuikSCAT winds in combination with some of the most widely used gas transfer velocity parameterizations. Results show that net CO2 flux estimations during an entire seasonal cycle (September 2002–September 2003) may vary by a factor of ~ 3 depending on the selected wind speed product and the gas exchange parameterization, with the highest impact due to the last one. The comparison of satellite- and model-derived winds with observations at buoys advises against the systematic overestimation of NCEP-2 and the underestimation of NCEP-1. In the coastal region, the presence of land and the time resolution are the main constraints of QuikSCAT, which turns CCMP and ERA-Interim in the preferred options.

Global ocean carbon uptake: magnitude, variability and trends

Abstract. The globally integrated sea–air anthropogenic carbon dioxide (CO2) flux from 1990 to 2009 is determined from models and data-based approaches as part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project. Numerical methods include ocean inverse models, atmospheric inverse models, and ocean general circulation models with parameterized biogeochemistry (OBGCMs). The median value of different approaches shows good agreement in average uptake. The best estimate of anthropogenic CO2 uptake for the time period based on a compilation of approaches is −2.0 Pg C yr−1. The interannual variability in the sea–air flux is largely driven by large-scale climate re-organizations and is estimated at 0.2 Pg C yr−1 for the two decades with some systematic differences between approaches. The largest differences between approaches are seen in the decadal trends. The trends range from −0.13 (Pg C yr−1) decade−1 to −0.50 (Pg C yr−1) decade−1 for the two decades under investigation. The OBGCMs and the data-based sea–air CO2 flux estimates show appreciably smaller decadal trends than estimates based on changes in carbon inventory suggesting that methods capable of resolving shorter timescales are showing a slowing of the rate of ocean CO2 uptake. RECCAP model outputs for five decades show similar differences in trends between approaches.

Global surface-ocean &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;&amp;lt;/sup&amp;gt; and sea–air CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; flux variability from an observation-driven ocean mixed-layer scheme

Abstract. A temporally and spatially resolved estimate of the global surface-ocean CO2 partial pressure field and the sea–air CO2 flux is presented, obtained by fitting a simple data-driven diagnostic model of ocean mixed-layer biogeochemistry to surface-ocean CO2 partial pressure data from the SOCAT v1.5 database. Results include seasonal, interannual, and short-term (daily) variations. In most regions, estimated seasonality is well constrained from the data, and compares well to the widely used monthly climatology by Takahashi et al. (2009). Comparison to independent data tentatively supports the slightly higher seasonal variations in our estimates in some areas. We also fitted the diagnostic model to atmospheric CO2 data. The results of this are less robust, but in those areas where atmospheric signals are not strongly influenced by land flux variability, their seasonality is nevertheless consistent with the results based on surface-ocean data. From a comparison with an independent seasonal climatology of surface-ocean nutrient concentration, the diagnostic model is shown to capture relevant surface-ocean biogeochemical processes reasonably well. Estimated interannual variations will be presented and discussed in a companion paper.