Observing biogeochemical cycles at global scales with profiling floats and gliders: prospects for a global array

Chemical and biological sensor technologies have advanced rapidly in the past five years. Sensors that require low power and operate for multiple years are now available for oxygen, nitrate, and a variety of bio-optical properties that serve as proxies for important components of the carbon cycle (e.g., particulate organic carbon). These sensors have all been deployed successfully for long periods, in some cases more than three years, on platforms such as profiling floats or gliders. Technologies for pH, pCO2, and particulate inorganic carbon are maturing rapidly as well. These sensors could serve as the enabling technology for a global biogeochemical observing system that might operate on a scale comparable to the current Argo array. Here, we review the scientific motivation and the prospects for a global observing system for ocean biogeochemistry

Coupling the PLANKTOM5.0 marine ecosystem model to the OCCAM 1º ocean general circulation model for investigation of the sensitivity of global biogeochemical cycles to variations in ecosystem complexity and physical environment

The earliest marine ecosystem models consisted of a simple representation of the main features of marine ecosystems, including, typically, variables for phytoplankton, zooplankton, nutrient and detritus (NPZD models). These have been incorporated into ocean general circulation models to give a basic representation of ecosystem function, providing predictions of bulk quantities such as global primary production, export and biomass which can be compared with available observations. A recent trend has been to increase the number of phytoplankton and zooplankton groups modelled, as analogues of different plankton groups observed to exist in the ocean, for example diatoms and cocolithophores (the so-called plankton functional type or PFT approach). It is usually assumed that the increase in complexity of the model will result in simulated ecosystems which more faithfully reproduce observations than NPZD models, but this has not been demonstrated systematically. The robustness of the PFT models to changes in model parameters and to changes to the physical environment in which it is embedded, have not been investigated. As a first step towards these goals, we incorporate a state-of-the-art PFT model, PLANKTOM5.0 into the OCCAM ocean general circulation model. A 6 year simulation is performed, covering the years 1989-1994 with identical parameter choices to an existing run of PLANKTOM5.0 coupled to the OPA general circulation model. This document describes the development of the coupled model and the 6 year simulation. Comparison with the OPA model and sensitivity of the solution to parameter choices will be described in a forthcoming journal paper

Recent variability of the global ocean carbon sink

We present a new observation-based estimate of the global oceanic carbon dioxide (CO2) sink and its temporal variation on a monthly basis from 1998 through 2011 and at a spatial resolution of 1×1. This sink estimate rests upon a neural network-based mapping of global surface ocean observations of the partial pressure of CO2 (pCO2) from the Surface Ocean CO2 Atlas database. The resulting pCO2 has small biases when evaluated against independent observations in the different ocean basins, but larger randomly distributed differences exist particularly in high latitudes. The seasonal climatology of our neural network-based product agrees overall well with the Takahashi et al. (2009) climatology, although our product produces a stronger seasonal cycle at high latitudes. From our global pCO2 product, we compute a mean net global ocean (excluding the Arctic Ocean and coastal regions) CO2 uptake flux of −1.42 ± 0.53 Pg C yr−1, which is in good agreement with ocean inversion-based estimates. Our data indicate a moderate level of interannual variability in the ocean carbon sink (±0.12 Pg C yr−1, 1𝜎) from 1998 through 2011, mostly originating from the equatorial Pacific Ocean, and associated with the El Nino–Southern Oscillation. Accounting for steady state riverine and Arctic Ocean carbon fluxes our estimate further implies a mean anthropogenic CO2 uptake of −1.99 ± 0.59 Pg C yr−1 over the analysis period. From this estimate plus the most recent estimates for fossil fuel emissions and atmospheric CO2 accumulation, we infer a mean global land sink of −2.82 ± 0.85 Pg C yr−1 over the 1998 through 2011 period with strong interannual variation

The Late Ordovician Biogeochemical Carbon Cycle

The isotopic composition of the carbonate carbon (δ13Ccarb) is one of the best tools for understanding the biogeochemical carbon cycle through Earth history. δ13Ccarb is also used to chemostratigraphically correlate coeval strata. This dissertation has three main foci that all utilize δ13Ccarb as the common data type. The geologic interval investigated was the Late Ordovician (458-444 Ma) with emphasis on the Guttenberg δ13C excursion, a globally correlated, positive ~3 / event that is ~400 kyr in duration. In the first topic we evaluate post-depositional alteration (i.e., diagenesis) of δ13Ccarb signals. In the second topic, we make reconstructions of sea level change using lithostratigraphic and δ13Ccarb chemostratigraphic correlations. In the third topic, we use box models to constrain the source of the Guttenberg δ13Ccarb excursion

The biogeochemical iron cycle and astrobiology

Biogeochemistry investigates chemical cycles which influence or are influenced by biological activity. Astrobiology studies the origin, evolution and distribution of life in the universe. The biogeochemical Fe cycle has controlled major nutrient cycles such as the C cycle throughout geological time. Iron sulfide minerals may have provided energy and surfaces for the first pioneer organisms on Earth. Banded iron formations document the evolution of oxygenic photosynthesis. To assess the potential habitability of planets other than Earth one looks for water, an energy source and a C source. On Mars, for example, Fe minerals have provided evidence for the past presence of liquid water on its surface and would provide a viable energy source. Here we present Mössbauer spectroscopy investigations of Fe and C cycle interactions in both ancient and modern environments. Experiments to simulate the diagenesis of banded iron formations indicate that the formation of ferrous minerals depends on the amount of biomass buried with ferric precursors rather than on the atmospheric composition at the time of deposition. Mössbauer spectra further reveal the mutual stabilisation of Fe-organic matter complexes against mineral transformation and decay of organic matter into CO2. This corresponds to observation of a ‘rusty carbon sink’ observed in modern sediments. The stabilisation of Fe-organic matter may also aid transport of particulate Fe in the water column while having on adverse effect on the bioavailability of Fe. In the modern oxic ocean, Fe is insoluble and particulate Fe represents an important source. Collecting that particulate Fe yields small sample sizes that would pose a challenge for conventional Mössbauer experiments. We demonstrate that the unique properties of the beam used in synchrotron-based Mössbauer applications can be utilized for studying such samples effectively. Reactive Fe species often occur in amorphous or nanoparticulate form in the environment and are therefore difficult to study with standard mineralogical tools. Sequential extraction techniques are commonly used as proxies. We provide an example where Mössbauer spectroscopy can replace sequential extraction techniques where mineralogical information is sought. Where mineral separation is needed, for example in the investigation of Fe or S isotope fractionation, Mössbauer spectroscopy can help to optimize sequential extraction procedures. This can be employed in large number of investigations of soils and sediments, potentially even for mineral separation to study Fe and S isotope fractionation in samples returned from Mars, which might reveal signatures of biological activity. When looking for the possibility of life outside Earth, Jupiter’s icy moon Europa is one of the most exciting places. It may be just in reach for a Mössbauer spectrometer deployed by a future lander to study the red streak mineral deposits on its surface to look for clues about the composition of the ocean hidden under the moon’s icy surface

The first-order effect of Holocene Northern Peatlands on global carbon cycle dynamics

Given the fact that the estimated present-day carbon storage of Northern Peatlands (NP) is about 300–500 petagram (PgC, 1 petagram = 1015 gram), and the NP has been subject to a slow but persistent growth over the Holocene epoch, it is desirable to include the NP in studies of Holocene carbon cycle dynamics. Here we use an Earth system Model of Intermediate Complexity to study the first-order effect of NP on global carbon cycle dynamics in the Holocene. We prescribe the reconstructed NP growth based on data obtained from numerous sites (located in Western Siberia, North America, and Finland) where peat accumulation records have been developed. Using an inverse method, we demonstrate that the long-term debates over potential source and/or sink of terrestrial ecosystem in the Holocene are clarified by using an inverse method, and our results suggest that the primary carbon source for the changes (sinks) of atmospheric and terrestrial carbon is the ocean, presumably, due to the deep ocean sedimentation pump (the so-called alkalinity pump). Our paper here complements ref. 1 by sensitivity tests using modified boundary conditions

Net community production in the North Atlantic Ocean derived from Volunteer Observing Ship data

The magnitude of marine plankton net community production (NCP) is indicative of both the biologically driven exchange of carbon dioxide between the atmosphere and the surface ocean and the export of organic carbon from the surface ocean to the ocean interior. In this study the seasonal variability in the NCP of five biogeochemical regions in the North Atlantic was determined from measurements of surface water dissolved oxygen and dissolved inorganic carbon (DIC) sampled from a Volunteer Observing Ship (VOS). The magnitude of NCP derived from dissolved oxygen measurements (NCPinline image) was consistent with previous geochemical estimates of NCP in the North Atlantic, with an average annual NCPinline image of 9.5 ± 6.5 mmol O2 m−2 d−1. Annual NCPinline image did not vary significantly over 35° of latitude and was not significantly different from NCP derived from DIC measurements (NCPDIC). The relatively simple method described here is applicable to any VOS route on which surface water dissolved oxygen concentrations can be accurately measured, thus providing estimates of NCP at higher spatial and temporal resolution than currently achieved