Estimating the monthly pCO2 distribution in the north Atlantic using a self-organizing neural network

Here we present monthly, basin-wide maps of the partial pressure of carbon dioxide (pCO2) for the North Atlantic on a 1° latitude by 1° longitude grid for years 2004 through 2006 inclusive. The maps have been computed using a neural network technique which reconstructs the non-linear relationships between three biogeochemical parameters and marine pCO 2. A self organizing map (SOM) neural network has been trained using 389 000 triplets of the SeaWiFS-MODIS chlorophyll-a concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. The trained SOM was labelled with 137 000 underway pCO2 measurements collected in situ during 2004, 2005 and 2006 in the North Atlantic, spanning the range of 208 to 437 µatm. The root mean square error (RMSE) of the neural network fit to the data is 11.6 µatm, which equals to just above 3 per cent of an average pCO2 value in the in situ dataset. The seasonal pCO2 cycle as well as estimates of the interannual variability in the major biogeochemical provinces are presented and discussed. High resolution combined with basin-wide coverage makes the maps a useful tool for several applications such as the monitoring of basin-wide air-sea CO2 fluxes or improvement of seasonal and interannual marine CO2 cycles in future model predictions. The method itself is a valuable alternative to traditional statistical modelling techniques used in geosciences

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

Can simple models predict large-scale surface ocean isoprene concentrations?

We use isoprene and related field measurements from three different ocean data sets together with remotely sensed satellite data to model global marine isoprene emissions. We show that using monthly mean satellite-derived chl a concentrations to parameterize isoprene with a constant chl a normalized isoprene production rate underpredicts the measured oceanic isoprene concentration by a mean factor of 19±12. Improving the model by using phytoplankton functional type dependent production values and by decreasing the bacterial degradation rate of isoprene in the water column results in only a slight underestimation (factor 1.7±1.2). We calculate global isoprene emissions of 0.21TgC for 2014 using this improved model, which is twice the value calculated using the original model. Nonetheless, the sea-to-air fluxes have to be at least 1 order of magnitude higher to account for measured atmospheric isoprene mixing ratios. These findings suggest that there is at least one missing oceanic source of isoprene and, possibly, other unknown factors in the ocean or atmosphere influencing the atmospheric values. The discrepancy between calculated fluxes and atmospheric observations must be reconciled in order to fully understand the importance of marine-derived isoprene as a precursor to remote marine boundary layer particle formation

ASSESSMENT OF THE QUALITY OF THE SHIPBOARD MEASUREMENTS OF TOTAL ALKALINITY ON THE WOCE HYDROGRAPHIC PROGRAM INDIAN OCEAN CO2 SURVEY CRUISES 1994-1996

In 1995, we participated in a number of WOCE Hydrographic Program cruises in the Indian Ocean as part of the Joint Global Ocean flux Study (JGOFS) CO, Survey sponsored by the Department of Energy (DOE). Two titration systems were used throughout this study to determine the pH, total alkalinity (TA) and total inorganic carbon dioxide (TCO2) of the samples collected during these cruises. The performance of these systems was monitored by making closed cell titration measurements on Certified Reference Materials (CRMs). A total of 962 titrations were made on six batches of CRMs during the cruises. The reproducibility calculated from these titrations was +/-0.007 in pH, +/-4.2 mu mol kg(-1) in TA, and +/-4.1 mu mol kg(-1) in TCO2. The at-sea measurements on the CRMs were in reasonable agreement with laboratory measurements made on the same batches. These results demonstrate that the CRMs can be used as a reference standard for TA and to monitor the performance of titration systems at sea. Measurements made on the various legs of the cruise agreed to within 6 mu mol kg(-1) at the 15 crossover points. The overall mean and standard deviation of the differences at all the crossovers are 2.1 +/- 2.1 mu mol kg(-1). These crossover results are quite consistent with the overall reproducibility of the CRM analyses for TA (+/-4 mu mol kg(-1)) over the duration of the entire survey, The TA results for the Indian Ocean cruises provide a reliable data set that when combined with TCO2 data can completely characterize the carbonate system. (C) 1998 Elsevier Science B.V. All rights reserved.X1120sciescopu