5 research outputs found
Bottom mixed layer oxygen dynamics in the Celtic Sea
The seasonally stratified continental shelf seas are highly productive, economically important environments which are under considerable pressure from human activity. Global dissolved oxygen concentrations have shown rapid reductions in response to anthropogenic forcing since at least the middle of the twentieth century. Oxygen consumption is at the same time linked to the cycling of atmospheric carbon, with oxygen being a proxy for carbon remineralisation and the release of CO2. In the seasonally stratified seas the bottom mixed layer (BML) is partially isolated from the atmosphere and is thus controlled by interplay between oxygen consumption processes, vertical and horizontal advection. Oxygen consumption rates can be both spatially and temporally dynamic, but these dynamics are often missed with incubation based techniques. Here we adopt a Bayesian approach to determining total BML oxygen consumption rates from a high resolution oxygen time-series. This incorporates both our knowledge and our uncertainty of the various processes which control the oxygen inventory. Total BML rates integrate both processes in the water column and at the sediment interface. These observations span the stratified period of the Celtic Sea and across both sandy and muddy sediment types. We show how horizontal advection, tidal forcing and vertical mixing together control the bottom mixed layer oxygen concentrations at various times over the stratified period. Our muddy-sand site shows cyclic spring-neap mediated changes in oxygen consumption driven by the frequent resuspension or ventilation of the seabed. We see evidence for prolonged periods of increased vertical mixing which provide the ventilation necessary to support the high rates of consumption observed
A BGC-Argo Guide: Planning, Deployment, Data Handling and Usage
The Biogeochemical-Argo program (BGC-Argo) is a new proïŹling-ïŹoat-based, ocean wide, and distributed ocean monitoring program which is tightly linked to, and has beneïŹted signiïŹcantly from, the Argo program. The community has recommended for BGC-Argo to measure six additional properties in addition to pressure, temperature and salinity measured by Argo, to include oxygen, pH, nitrate, downwelling light, chlorophyll ïŹuorescenceandtheopticalbackscatteringcoefïŹcient.Thepurposeofthisadditionisto enable the monitoring of ocean biogeochemistry and health, and in particular, monitor major processes such as ocean deoxygenation, acidiïŹcation and warming and their effect on phytoplankton, the main source of energy of marine ecosystems. Here we describe the salient issues associated with the operation of the BGC-Argo network, with information useful for those interested in deploying ïŹoats and using the data they produce. The topics include ïŹoat testing, deployment and increasingly, recovery. Aspects of data management, processing and quality control are covered as well as speciïŹc issues associated with each of the six BGC-Argo sensors. In particular, it is recommended that water samples be collected during ïŹoat deployment to be used for validation of sensor output
Global Carbon Budget 2020
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate â the âglobal carbon budgetâ â is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1Ï. For the last decade available (2010â2019), EFOS was 9.6â±â0.5âGtCâyrâ1 excluding the cement carbonation sink (9.4â±â0.5âGtCâyrâ1 when the cement carbonation sink is included), and ELUC was 1.6â±â0.7âGtCâyrâ1. For the same decade, GATM was 5.1â±â0.02âGtCâyrâ1 (2.4â±â0.01âppmâyrâ1), SOCEAN 2.5â±â 0.6âGtCâyrâ1, and SLAND 3.4â±â0.9âGtCâyrâ1, with a budget imbalance BIM of â0.1âGtCâyrâ1 indicating a near balance between estimated sources and sinks over the last decade. For the year 2019 alone, the growth in EFOS was only about 0.1â% with fossil emissions increasing to 9.9â±â0.5âGtCâyrâ1 excluding the cement carbonation sink (9.7â±â0.5âGtCâyrâ1 when cement carbonation sink is included), and ELUC was 1.8â±â0.7âGtCâyrâ1, for total anthropogenic CO2 emissions of 11.5â±â0.9âGtCâyrâ1 (42.2â±â3.3âGtCO2). Also for 2019, GATM was 5.4â±â0.2âGtCâyrâ1 (2.5â±â0.1âppmâyrâ1), SOCEAN was 2.6â±â0.6âGtCâyrâ1, and SLAND was 3.1â±â1.2âGtCâyrâ1, with a BIM of 0.3âGtC. The global atmospheric CO2 concentration reached 409.85â±â0.1âppm averaged over 2019. Preliminary data for 2020, accounting for the COVID-19-induced changes in emissions, suggest a decrease in EFOS relative to 2019 of about â7â% (median estimate) based on individual estimates from four studies of â6â%, â7â%, â7â% (â3â% to â11â%), and â13â%. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959â2019, but discrepancies of up to 1âGtCâyrâ1 persist for the representation of semi-decadal variability in CO2 fluxes. Comparison of estimates from diverse approaches and observations shows (1) no consensus in the mean and trend in land-use change emissions over the last decade, (2) a persistent low agreement between the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) an apparent discrepancy between the different methods for the ocean sink outside the tropics, particularly in the Southern Ocean. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set (Friedlingstein et al., 2019; Le QuĂ©rĂ© et al., 2018b, a, 2016, 2015b, a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2020 (Friedlingstein et al., 2020)