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humidity, we expect a 7% increase in atmospheric moisture content for every degree of 30 warming of the Earth's lower troposphere (2). Of greatest importance to society, and the focus 31 of this work, is the strength of the regional pattern of evaporation and precipitation (E--P), 32 which in climate models scales approximately with CC, while global precipitation changes more 33 slowly at a rate of 2--3% °C --1 (2, 4). 34An intensification of existing patterns of global mean surface evaporation and precipitation (E-- do not yet have a definitive view on whether the Earth's water cycle has intensified over the 61 past several decades from atmospheric observing networks (12,20). 62It has long been noted that the climatological mean sea surface salinity (SSS) spatial pattern is 63 highly correlated with the long--term mean E--P spatial pattern (21) ( estimates of long--term SSS change (24, 25, 27). Following the "rich get richer" mechanism (7) Table S2). Our examples of the simulations 117 that most closely replicate the observed spatial change and mean patterns (Fig. 1E, H) and 118 those that produce an almost inverse spatial change pattern (Fig. 1F, I) compared to the 119 observed results (Fig. 1D, G), illustrate the range of responses found in CMIP3 (Fig. 1). Some 120 models show similar numbers to those observed (Fig. 1E, H The PA and PC methodology can also be used when considering other variables, such as the 126 surface water flux (E--P). CMIP3 simulations show a relationship between SSS PA and the E--P PA 127 (Fig. 2B). This key result supports the use of SSS PA as a diagnostic of a changing water cycle, 128 and also provides a relationship in which to consider the observed SSS PA for 1950--2000. The 129CMIP3 SSS patterns amplify at twice the rate of E--P patterns (Fig. 2B) Figure S9). 136For both the 20C3M and SRES CMIP3 simulations, we find a clear relationship between the rate 137 of global average surface warming (ΔTa) and the rate of SSS PA and PC strength ( Fig. 2A). 13820C3M simulations in which the warming rate is low (generally those with comprehensive 139 aerosol schemes; contrast diamonds and circles in Fig. S5; Table S1) suggests that SSS patterns intensify with warming at 8% °C --1 ( Fig. 2A), which is half of our 1950--147 2000 observed rate (16% °C --1 ; Fig. 2A). As expected, based on past analyses of CMIP3 (2), the E--148 P PA is also linearly related to surface warming rates (Fig. 2C) surface water flux, near 3.1% °C --1 (Fig. 2D). The stronger SSS PA response to warming and 152 tighter agreement among CMIP3 when compared to that for the E--P PA ( Fig. 2A vs C To independently demonstrate the strong relationship between 50--year salinity change and an 159 enhanced water cycle, the response of an ocean--only model to an idealised 5% E--P pattern 160 increase was explored. We used a version of the MOM3 ocean model, forced with E--P fields 161 obtained from the NCEP reanalysis. A linear trend in E--P was imposed to achieve a 5% increase (which shows that SSS PA increases at twice the rat...

[1] We examine six different coupled climate model simulations to determine the ocean biological response to climate warming between the beginning of the industrial revolution and 2050. We use vertical velocity, maximum winter mixed layer depth, and sea ice cover to define six biomes. Climate warming leads to a contraction of the highly productive marginal sea ice biome by 42% in the Northern Hemisphere and 17% in the Southern Hemisphere, and leads to an expansion of the low productivity permanently stratified subtropical gyre biome by 4.0% in the Northern Hemisphere and 9.4% in the Southern Hemisphere. In between these, the subpolar gyre biome expands by 16% in the Northern Hemisphere and 7% in the Southern Hemisphere, and the seasonally stratified subtropical gyre contracts by 11% in both hemispheres. The low-latitude (mostly coastal) upwelling biome area changes only modestly. Vertical stratification increases, which would be expected to decrease nutrient supply everywhere, but increase the growing season length in high latitudes. We use satellite ocean color and climatological observations to develop an empirical model for predicting chlorophyll from the physical properties of the global warming simulations. Four features stand out in the response to global warming: (1) a drop in chlorophyll in the North Pacific due primarily to retreat of the marginal sea ice biome, (2) a tendency toward an increase in chlorophyll in the North Atlantic due to a complex combination of factors, (3) an increase in chlorophyll in the Southern Ocean due primarily to the retreat of and changes at the northern boundary of the marginal sea ice zone, and (4) a tendency toward a decrease in chlorophyll adjacent to the Antarctic continent due primarily to freshening within the marginal sea ice zone. We use three different primary production algorithms to estimate the response of primary production to climate warming based on our estimated chlorophyll concentrations. The three algorithms give a global increase in primary production of 0.7% at the low end to 8.1% at the high end, with very large regional differences. The main cause of both the response to warming and the variation between algorithms is the temperature sensitivity of the primary production algorithms. We also show results for the period between the industrial revolution and 2050 and 2090.

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. ) substantially since preindustrial times (1-3). These changes, particularly with respect to carbonate ion, strongly vary between ocean basins. Over the 21st century, the carbonate ion levels over most of the surface ocean are expected to remain supersaturated with respect to aragonite (2, 3), the more soluble form of calcium carbonate. Despite this, studies have demonstrated that calcifying organisms depend on variations in aragonite saturation state (3-5). Aragonite saturation in seawater allows marine organisms to adequately secrete and accumulate this carbonate mineral during growth and development. The Southern Ocean (south of 60°S), however, is predicted to begin to experience aragonite undersaturation by the year 2050 if assuming surface ocean CO 2 equilibrium with the atmosphere, while most ocean models suggest that mean surface conditions throughout the Southern Ocean will become undersaturated by the year 2100 (3). Aragonite undersaturation both enhances the dissolution of aragonite and reduces formation of aragonite shells of marine organisms (4-7), making the prediction of aragonite undersaturation by the end of this century of particular concern to the Southern Ocean marine ecosystem. Systematic natural seasonal variations of pH and CO 3 2Ϫ can either amplify or depress the onset of future ocean acidification and aragonite undersaturation. Although seasonal variability has been suggested to hasten the onset of aragonite undersaturation (3), observational evidence in the Southern Ocean has...

[1] Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (±1s) downward flux of organic matter across 75 m depth is 17 ± 6 Pg C yr À1 . Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.

A B S T R A C TThe distribution of anthropogenic carbon (C ant ) in the oceans is estimated using the transit time distribution (TTD) method applied to global measurements of chlorofluorocarbon-12 (CFC12). Unlike most other inference methods, the TTD method does not assume a single ventilation time and avoids the large uncertainty incurred by attempts to correct for the large natural carbon background in dissolved inorganic carbon measurements. The highest concentrations and deepest penetration of anthropogenic carbon are found in the North Atlantic and Southern Oceans. The estimated total inventory in 1994 is 134 Pg-C. To evaluate uncertainties the TTD method is applied to output from an ocean general circulation model (OGCM) and compared the results to the directly simulated C ant . Outside of the Southern Ocean the predicted C ant closely matches the directly simulated distribution, but in the Southern Ocean the TTD concentrations are biased high due to the assumption of 'constant disequilibrium'. The net result is a TTD overestimate of the global inventory by about 20%. Accounting for this bias and other centred uncertainties, an inventory range of 94-121 Pg-C is obtained. This agrees with the inventory of Sabine et al., who applied the C * method to the same data. There are, however, significant differences in the spatial distributions: The TTD estimates are smaller than C * in the upper ocean and larger at depth, consistent with biases expected in C * given its assumption of a single parcel ventilation time.

[1] In the Earth's geological record massive marine ecological change has been attributed to the occurrence of widespread anoxia in the ocean [Jahren, 2002;White, 2002;Wignall and Twitchett, 1996]. Climate change projection till the end of this century predict a 4 to 7% decline in the dissolve oxygen in the ocean [Bopp et al., 2002;Matear et al., 2000;Plattner et al., 2001;Sarmiento et al., 1998] suggesting the potential for global warming to eventually drive the deep ocean anoxic. To examine the multicentury impact of protracted global warming on oceanic concentrations of dissolved oxygen, we use a climate system model and a low-order oceanic biogeochemical model. The models are integrated for an atmospheric equivalent CO 2 concentration, which is specified to triple according to a standard scenario from the late nineteenth to the late twenty-first century, and then is subsequently held constant at that elevated level for an additional 6 centuries. For the present day, the model successfully reproduced the large-scale features of the dissolved oxygen field in the ocean. In the global warming simulation, the physical model displays marked changes in high-latitude oceanic stratification and overturning, including near-cessation of deep water renewal for depths greater than about 1.5 km during the period of elevated stable CO 2 concentration. Our model predicts a decline in oxygen concentration through most of the subsurface ocean. Concentration changes in the thermocline waters result mainly from solubility changes in the upstream source waters, while changes in the deep waters result mainly from lack of ventilation and ongoing consumption of oxygen by remineralization of sinking particulate organic matter. Changes in the upper 2 km of the ocean generally show signs of equilibration by the end of the integration, but at greater depths, there occurs a slow but steady decline through to the end of the integration. By the end of the integration, we simulate a doubling of the volume of hypoxic water (less than 10 mmol/kg) in the thermocline of the eastern equatorial Pacific Ocean. During the integration deep ocean oxygen concentrations generally decline by between 20 and 40%, but, significantly, no extensive deep ocean anoxia develops during the period of integration, nor does it appear that it would likely do so for at least a further 4000 years of integration. Subsurface oxygen decline is moderated by an overall reduction in export production of particulate organic matter, which reduces oxygen consumption in the ocean interior due to the remineralization of this material. Citation: Matear, R. J., and A. C. Hirst, Long-term changes in dissolved oxygen concentrations in the ocean caused by protracted global warming, Global Biogeochem.

We compared the 13 models participating in the Ocean Carbon Model Intercomparison Project (OCMIP) with regards to their skill in matching observed distributions of CFC-11. This analysis characterizes the abilities of these models to ventilate the ocean on timescales relevant for anthropogenic CO uptake. We found a large range in the modeled global inventory (AE30%), mainly due to differences in ventilation from the high latitudes. In the Southern Ocean, models differ particularly in the longitudinal distribution of the CFC uptake in the intermediate water, whereas the latitudinal distribution is mainly controlled by the subgrid-scale parameterization. Models with isopycnal diffusion and eddy-induced velocity parameterization produce more realistic intermediate water ventilation. Deep and bottom water ventilation also varies substantially between the models. Models coupled to a sea-ice model systematically provide more realistic AABW formation source region; however these same models also largely overestimate AABW ventilation if no specific parameterization of brine rejection during sea-ice formation is included. In the North Pacific Ocean, all models exhibit a systematic large underestimation of the CFC uptake in the thermocline of the subtropical gyre, while no systematic difference toward the observations is found in the subpolar gyre. In the North Atlantic Ocean, the CFC uptake is globally underestimated in subsurface. In the deep ocean, all but the adjoint model, failed to produce the two recently ventilated branches observed in the North Atlantic Deep Water (NADW). Furthermore, simulated transport in the Deep Western Boundary Current (DWBC) is too sluggish in all but the isopycnal model, where it is too rapid. Ó