Global ocean storage of anthropogenic carbon

48 páginas, 7 figuras, 7 tablas. -- S. Kathiwala ... et al.-- Proyecto CarbochangeThe global ocean is a significant sink for anthropogenic carbon (Cant), absorbing roughly a third of human CO2 emitted over the industrial period. Robust estimates of the magnitude and variability of the storage and distribution of Cant in the ocean are therefore important for understanding the human impact on climate. In this synthesis we review observational and model-based estimates of the storage and transport of Cant in the ocean. We pay particular attention to the uncertainties and potential biases inherent in different inference schemes. On a global scale, three data based estimates of the distribution and inventory of Cant are now available. While the inventories are found to agree within their uncertainty, there are considerable differences in the spatial distribution. We also present a review of the progress made in the application of inverse and data-assimilation techniques which combine ocean interior estimates of Cant with numerical ocean circulation models. Such methods are especially useful for estimating the air-sea flux and interior transport of Cant, quantities that are otherwise difficult to observe directly. However, the results are found to be highly dependent on modeled circulation, with the spread due to different ocean models at least as large as that from the different observational methods used to estimate Cant. Our review also highlights the importance of repeat measurements of hydrographic and biogeochemical parameters to estimate the storage of Cant on decadal timescales in the presence of the variability in circulation that is neglected by other approaches. Data-based Cant estimates provide important constraints on ocean forward models, which exhibit both broad similarities and regional errors relative to the observational fields. A compilation of inventories of Cant gives us a "best" estimate of the global ocean inventory of anthropogenic carbon in 2010 of 155 Pg C with an uncertainty of ±20%. This estimate includes a broad range of values suggesting that a combination of approaches is necessary in order to achieve a robust quantification of the ocean sink of anthropogenic CO2.Peer reviewe

Changes to the air‐sea flux and distribution of radiocarbon in the ocean over the 21st century

We investigate the spatiotemporal evolution of radiocarbon (Δ14C) in the ocean over the 21st century under different scenarios for anthropogenic CO2 emissions and atmospheric CO2 and radiocarbon changes using a 3‐D ocean carbon cycle model. Strong decreases in atmospheric Δ14C in the high‐emission scenario result in strong outgassing of 14C over 2050–2100, causing Δ14C spatial gradients in the surface ocean and vertical gradients between the surface and intermediate waters to reverse sign. Surface Δ14C in the subtropical gyres is lower than Δ14C in Pacific Deep Water and Southern Ocean surface water in 2100. In the low‐emission scenario, ocean Δ14C remains slightly higher than in 1950 and relatively constant over 2050–2100. Over the next 20 years we find decadal changes in Δ14C of −30‰ to +5‰ in the upper 2 km of the ocean, which should be detectable with continued hydrographic surveys. Our simulations can help in planning future observations, and they provide a baseline for investigating natural or anthropogenic changes in ocean circulation using ocean Δ14C observations and models

Future changes in δ 13 C of dissolved inorganic carbon in the ocean

Emissions of carbon dioxide from fossil fuel combustion are reducing the ratio 13C/12C, δ13C, in atmospheric urn:x-wiley:23284277:media:eft2900:eft2900-math-0001 and in the carbon in the ocean and terrestrial biosphere that exchanges with the atmosphere on timescales of decades to centuries. Future changes to fossil fuel emissions vary across different scenarios and may cause decreases of more than 6‰ in atmospheric δ13urn:x-wiley:23284277:media:eft2900:eft2900-math-0002 between 1850 and 2100. The effects of these potential changes on the three-dimensional distribution of δ13C in the ocean has not yet been investigated. Here, we use an ocean biogeochemical-circulation model forced with a range of Shared Socioeconomic Pathway (SSP)-based scenarios to simulate δ13C in ocean dissolved inorganic carbon from 1850 to 2100. In the future, vertical δ13C gradients characteristic of the biological pump are reduced or reversed, relative to the preindustrial period, with the reversal occurring in higher emission scenarios. For the highest emission scenario, SSP5-8.5, surface δ13C in the centre of Pacific subtropical gyres falls from 2.2‰ in 1850 to -3.5‰ by 2100. In lower emission scenarios, δ13C in the surface ocean decreases but then rebounds. The relationship between anthropogenic carbon (Cant) and δ13C in the ocean shows a larger scatter in all scenarios, suggesting that errors in δ13C-based estimates of Cant may increase in the future. These simulations were run with fixed physical forcing and ocean circulation, providing a baseline of predicted δ13C. Further work is needed to investigate the impact of climate-carbon cycle feedbacks on ocean δ13C changes

Chromophoric signatures of microbial by-products in the dark ocean

En prensa3,792

Water mass age and ageing driving chromophoric dissolved organic matter in the dark global ocean

Research articleThe omnipresence of chromophoric dissolved organic matter (CDOM) in the open ocean enables its use as a tracer for biochemical processes throughout the global overturning circulation. We made an inventory of CDOM optical properties, ideal water age (τ), and apparent oxygen utilization (AOU) along the Atlantic, Indian, and Pacific Ocean waters sampled during the Malaspina 2010 expedition. A water mass analysis was applied to obtain intrinsic, hereinafter archetypal, values of τ, AOU, oxygen utilization rate (OUR), and CDOM absorption coefficients, spectral slopes and quantum yield for each one of the 22 water types intercepted during this circumnavigation. Archetypal values of AOU and OUR have been used to trace the differential influence of water mass aging and aging rates, respectively, on CDOM variables. Whereas the absorption coefficient at 325nm (a325) and the fluorescence quantum yield at 340nm (Φ340) increased, the spectral slope over the wavelength range 275–295nm (S275–295) and the ratio of spectral slopes over the ranges 275–295nm and 350–400nm (SR) decreased significantly with water mass aging (AOU). Combination of the slope of the linear regression between archetypal AOU and a325 with the estimated global OUR allowed us to obtain a CDOM turnover time of 634 ± 120 years, which exceeds the flushing time of the dark ocean (>200 m) by 46%. This positive relationship supports the assumption of in situ production and accumulation of CDOM as a by-product of microbial metabolism as water masses turn older. Furthermore, our data evidence that global-scale CDOM quantity (a325) is more dependent on aging (AOU), whereas CDOM quality (S275–295, SR, Φ340) is more dependent on aging rate (OUR).Versión del editor4,785

The western North Atlantic shelfbreak current system in summer

Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography. 37 (2007): 2509-2533, doi:10.1175/JPO3123.1.Twelve years of historical hydrographic data, spanning the period 1990–2001, are analyzed to examine the along-stream evolution of the western North Atlantic Ocean shelfbreak front and current, following its path between the west coast of Greenland and the Middle Atlantic Bight. Over 700 synoptic sections are used to construct a mean three-dimensional description of the summer shelfbreak front and to quantify the along-stream evolution in properties, including frontal strength and grounding position. Results show that there are actually two fronts in the northern part of the domain—a shallow front located near the shelf break and a deeper front centered in the core of Irminger Water over the upper slope. The properties of the deeper Irminger front erode gradually to the south, and the front disappears entirely near the Grand Banks of Newfoundland. The shallow shelfbreak front is identifiable throughout the domain, and its properties exhibit large variations from north to south, with the largest changes occurring near the Tail of the Grand Banks. Despite these structural changes, and large variations in topography, the foot of the shelfbreak front remains within 20 km of the shelf break. The hydrographic sections are also used to examine the evolution of the baroclinic velocity field and its associated volume transport. The baroclinic velocity structure consists of a single velocity core that is stronger and penetrates deeper where the Irminger front is present. The baroclinic volume transport decreases by equal amounts at the southern end of the Labrador Shelf and at the Tail of the Grand Banks. Overall, the results suggest that the Grand Banks is a geographically critical location in the North Atlantic shelfbreak system.This work was supported by the National Science Foundation under Grants OCE00- 95261 (PF) and OCE-0450658 (RP)

Reconstruction of the history of anthropogenic CO2 concentrations in the ocean

The release of fossil fuel CO(2) to the atmosphere by human activity has been implicated as the predominant cause of recent global climate change. The ocean plays a crucial role in mitigating the effects of this perturbation to the climate system, sequestering 20 to 35 per cent of anthropogenic CO(2) emissions. Although much progress has been made in recent years in understanding and quantifying this sink, considerable uncertainties remain as to the distribution of anthropogenic CO(2) in the ocean, its rate of uptake over the industrial era, and the relative roles of the ocean and terrestrial biosphere in anthropogenic CO(2) sequestration. Here we address these questions by presenting an observationally based reconstruction of the spatially resolved, time-dependent history of anthropogenic carbon in the ocean over the industrial era. Our approach is based on the recognition that the transport of tracers in the ocean can be described by a Green's function, which we estimate from tracer data using a maximum entropy deconvolution technique. Our results indicate that ocean uptake of anthropogenic CO(2) has increased sharply since the 1950s, with a small decline in the rate of increase in the last few decades. We estimate the inventory and uptake rate of anthropogenic CO(2) in 2008 at 140 +/- 25 Pg C and 2.3 +/- 0.6 Pg C yr(-1), respectively. We find that the Southern Ocean is the primary conduit by which this CO(2) enters the ocean (contributing over 40 per cent of the anthropogenic CO(2) inventory in the ocean in 2008). Our results also suggest that the terrestrial biosphere was a source of CO(2) until the 1940s, subsequently turning into a sink. Taken over the entire industrial period, and accounting for uncertainties, we estimate that the terrestrial biosphere has been anywhere from neutral to a net source of CO(2), contributing up to half as much CO(2) as has been taken up by the ocean over the same period