Peter E. Land

Optical modeling and measurements of a coccolithophore bloom

Blooms of the phytoplankton coccolithophorid Emiliania huxleyi can cause significant changes to both the inherent and the apparent optical properties within an oceanic column. Measurements made within such a bloom off the southwestern coast of England during July 1999 are reported. The multiple scattering properties of the bloom prevented accurate retrieval of absorption (a) and attenuation (c) coefficients with a WETLabs ac-9. Upwelling radiance measurements were similarly affected by the bloom, which caused the sensors to saturate. An optical model has been developed that gives close agreement with the in situ optics when it is used as input to the Hydrolight radiative-transfer model.

A near‐real time automatic MODIS data processing system

The Moderate Resolution Imaging Spectroradiometer (MODIS) on‐board the Aqua and Terra platforms was designed to improve understanding of global dynamics and processes occurring on the land, in the oceans, and in the lower atmosphere. The UK Dundee Satellite Receiving Station has two X‐band receiving systems capable of capturing direct broadcast data from these spacecraft with a range covering the European shelf‐areas, north‐east Atlantic ocean and the western Mediterranean Sea. Raw data are transferred to the Plymouth Marine Laboratory (PML) and processed in near‐real time into ocean colour and sea‐surface temperature products for the academic community. Data can be used operationally and are made available through the web within 1.5 hours of the satellite overpass time. To our knowledge this is the only such developed system in Europe producing near‐real time MODIS ocean colour products.

Exploiting satellite earth observation to quantify current global oceanic DMS flux and its future climate sensitivity

We used coincident Envisat RA2 and AATSR temperature and wind speed data from 2008/2009 to calculate the global net sea-air flux of dimethyl sulfide (DMS), which we estimate to be 19.6 Tg S a−1. Our monthly flux calculations are compared to open ocean eddy correlation measurements of DMS flux from 10 recent cruises, with a root mean square difference of 3.1 μmol m−2 day−1. In a sensitivity analysis, we varied temperature, salinity, surface wind speed, and aqueous DMS concentration, using fixed global changes as well as CMIP5 model output. The range of DMS flux in future climate scenarios is discussed. The CMIP5 model predicts a reduction in surface wind speed and we estimate that this will decrease the global annual sea-air flux of DMS by 22% over 25 years. Concurrent changes in temperature, salinity, and DMS concentration increase the global flux by much smaller amounts. The net effect of all CMIP5 modelled 25 year predictions was a 19% reduction in global DMS flux. 25 year DMS concentration changes had significant regional effects, some positive (Southern Ocean, North Atlantic, Northwest Pacific) and some negative (isolated regions along the Equator and in the Indian Ocean). Using satellite-detected coverage of coccolithophore blooms, our estimate of their contribution to North Atlantic DMS emissions suggests that the coccolithophores contribute only a small percentage of the North Atlantic annual flux estimate, but may be more important in the summertime and in the northeast Atlantic.

FluxEngine: A Flexible Processing System for Calculating Atmosphere–Ocean Carbon Dioxide Gas Fluxes and Climatologies

Theair‐seafluxofgreenhousegases[e.g.,carbondioxide(CO2)]isacriticalpartoftheclimatesystemanda major factor in the biogeochemical development of the oceans. More accurate and higher-resolution calculations of these gas fluxes are required if researchers are to fully understand and predict future climate. Satellite Earth observation is able to provide large spatial-scale datasets that can be used to study gas fluxes. However, the large storage requirements needed to host such data can restrict its use by the scientific community. Fortunately, the development of cloud computing can provide a solution. This paper describes an open-source air‐sea CO2 flux processing toolbox called the ‘‘FluxEngine,’’ designed for use on a cloudcomputing infrastructure. The toolbox allows users to easily generate global and regional air‐sea CO2 flux data from model, in situ, and Earth observation data, and its air‐sea gas flux calculation is user configurable. Its current installation on the Nephalae Cloud allows users to easily exploit more than 8 TB of climate-quality Earth observation data for the derivation of gas fluxes. The resultant netCDF data outputfiles contain.20 data layerscontainingthevariousstagesofthefluxcalculationalongwithprocessindicatorlayerstoaidinterpretation of the data. This paper describes the toolbox design, which verifies the air‐sea CO2 flux calculations; demonstrates the use of the tools for studying global and shelf sea air‐sea fluxes; and describes future developments.

On the calculation of air‐sea fluxes of CO2 in the presence of temperature and salinity gradients

The presence of vertical temperature and salinity gradients in the upper ocean and the occurrence of variations in temperature and salinity on time scales from hours to many years complicate the calculation of the flux of carbon dioxide (CO2) across the sea surface. Temperature and salinity affect the interfacial concentration of aqueous CO2 primarily through their effect on solubility with lesser effects related to saturated vapor pressure and the relationship between fugacity and partial pressure. The effects of temperature and salinity profiles in the water column and changes in the aqueous concentration act primarily through the partitioning of the carbonate system. Climatological calculations of flux require attention to variability in the upper ocean and to the limited validity of assuming “constant chemistry” in transforming measurements to climatological values. Contrary to some recent analysis, it is shown that the effect on CO2 fluxes of a cool skin on the sea surface is large and ubiquitous. An opposing effect on calculated fluxes is related to the occurrence of warm layers near the surface; this effect can be locally large but will usually coincide with periods of low exchange. A salty skin and salinity anomalies in the upper ocean also affect CO2 flux calculations, though these haline effects are generally weaker than the thermal effects.

Salinity from Space Unlocks Satellite-Based Assessment of Ocean Acidification

Approximately a quarter of the carbon dioxide (CO2) that we emit into the atmosphere is absorbed by the ocean. This oceanic uptake of CO2 leads to a change in marine carbonate chemistry resulting in a decrease of seawater pH and carbonate ion concentration, a process commonly called ‘Ocean Acidification’. Salinity data are key for assessing the marine carbonate system, and new space-based salinity measurements will enable the development of novel space-based ocean acidification assessment. Recent studies have highlighted the need to develop new in situ technology for monitoring ocean acidification, but the potential capabilities of space-based measurements remain largely untapped. Routine measurements from space can provide quasi-synoptic, reproducible data for investigating processes on global scales; they may also be the most efficient way to monitor the ocean surface. As the carbon cycle is dominantly controlled by the balance between the biological and solubility carbon pumps, innovative methods to exploit existing satellite sea surface temperature and ocean color, and new satellite sea surface salinity measurements, are needed and will enable frequent assessment of ocean acidification parameters over large spatial scales.

A Sensitivity Analysis of the Impact of Rain on Regional and Global Sea-Air Fluxes of CO2

The global oceans are considered a major sink of atmospheric carbon dioxide (CO2). Rain is known to alter the physical and chemical conditions at the sea surface, and thus influence the transfer of CO2 between the ocean and atmosphere. It can influence gas exchange through enhanced gas transfer velocity, the direct export of carbon from the atmosphere to the ocean, by altering the sea skin temperature, and through surface layer dilution. However, to date, very few studies quantifying these effects on global net sea-air fluxes exist. Here, we include terms for the enhanced gas transfer velocity and the direct export of carbon in calculations of the global net sea-air fluxes, using a 7-year time series of monthly global climate quality satellite remote sensing observations, model and in-situ data. The use of a non-linear relationship between the effects of rain and wind significantly reduces the estimated impact of rain-induced surface turbulence on the rate of sea-air gas transfer, when compared to a linear relationship. Nevertheless, globally, the rain enhanced gas transfer and rain induced direct export increase the estimated annual oceanic integrated net sink of CO2 by up to 6%. Regionally, the variations can be larger, with rain increasing the estimated annual net sink in the Pacific Ocean by up to 15% and altering monthly net flux by > ± 50%. Based on these analyses, the impacts of rain should be included in the uncertainty analysis of studies that estimate net sea-air fluxes of CO2 as the rain can have a considerable impact, dependent upon the region and timescale.

Operational monitoring and forecasting of bathing water quality through exploiting satellite Earth observation and models

Coastal zones and shelf-seas are important for tourism, commercial fishing and aquaculture. As a result the importance of good water quality within these regions to support life is recognised worldwide and a number of international directives for monitoring them now exist. This paper describes the AlgaRisk water quality monitoring demonstration service that was developed and operated for the UK Environment Agency in response to the microbiological monitoring needs within the revised European Union Bathing Waters Directive. The AlgaRisk approach used satellite Earth observation to provide a near-real time monitoring of microbiological water quality and a series of nested operational models (atmospheric and hydrodynamic-ecosystem) provided a forecast capability. For the period of the demonstration service (2008-2013) all monitoring and forecast datasets were processed in near-real time on a daily basis and disseminated through a dedicated web portal, with extracted data automatically emailed to agency staff. Near-real time data processing was achieved using a series of supercomputers and an Open Grid approach. The novel web portal and java-based viewer enabled users to visualise and interrogate current and historical data. The system description, the algorithms employed and example results focussing on a case study of an incidence of the harmful algal bloom Karenia mikimotoi are presented. Recommendations and the potential exploitation of web services for future water quality monitoring services are discussed. Successful development of a coastal microbiological water quality monitoring and forecasting system (called AlgaRisk).System exploits satellite Earth observation and model forecasts to guide decisions and in situ sampling.Operational system run for 6 years (2008-2013) to support decision making within UK Environment Agency.System exploits open grid and supercomputing approaches and disseminated all data via a web interface and email.

Correction of Sensor Saturation Effects in MODIS Oceanic Particulate Inorganic Carbon

The highly reflective nature of high particulate inorganic carbon (PIC) from calcifying plankton, such as surface blooms of Emiliana huxleyi in the latter stages of their life cycle, can cause the saturation of the Moderate Resolution Imaging Spectrometer (MODIS) visible spectrum ocean color bands. This saturation results in errors in the standard MODIS oceanic PIC product, resulting in the highest PIC levels being represented as cloud-like gaps (missing data) in daily level 2 data, and as either gaps or erroneously low PIC values in temporally averaged data (e.g., 8-day level 3 data). A method is described to correct this error and to reconstruct the missing data in the ocean color band data by regressing the 1-km spatial resolution ocean color bands against MODIS higher resolution (500 m spatial resolution) bands with lower sensitivities. The method is applied to all North Atlantic MODIS data from 2002 to 2014. This shows the effect on mean PIC concentration over the whole North Atlantic to be less than 1% annually and 2% monthly, but with more significant regional effects, exceeding 10% in peak months in some coastal shelf regions. Effects are highly localized and tend to annually reoccur in similar geographical locations. Ignoring these missing data within intense blooms is likely to result in an underestimation of the influence that coccolithophores, and their changing distributions, are having on the North Atlantic carbon cycle. We see no evidence in this 12-year time series of a temporal poleward movement of these intense bloom events.

Remote sensing of surface ocean PH exploiting sea surface salinity satellite observations

The overall process commonly referred to as Ocean Acidification (OA) is nowadays gathering increasing attention for its profound impact at scientific and socio-economic level. To date, the majority of the scientific studies into the potential impacts of OA have focused on models and in situ datasets. Satellite remote sensing technology have yet to be fully exploited and could play a significant role by providing synoptic and frequent measurements for investigating OA processes on global scales. Within this context, the purpose of the ESA “Pathfinders-OA” project is to quantitatively and routinely estimate surface ocean pH by means of satellite observations in several ocean regions. Satellite Ocean Colour, Sea Surface Temperature and Sea Surface Salinity data (with an emphasis on the latter) will be exploited. A proper merging of these different datasets will allow to compute at least two independent proxies among the seawater carbonate system parameters and therefore obtain the best educated guess of the surface ocean pH. Preliminary results of the anomaly and variability of the ocean pH maps are presented.