Dark Ocean Research Articles

Drivers of fluorescent dissolved organic matter in the global epipelagic ocean

AbstractFluorescent dissolved organic matter (FDOM) in open surface waters (< 200 m) of the Atlantic, Pacific, and Indian oceans was analysed by excitation‐emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC). A four‐component PARAFAC model was fit to the EEMs, which included two humic‐ (C1 and C2) and two amino acid‐like (C3 and C4) components previously identified in ocean waters. Generalized‐additive models (GAMs) were used to explore the environmental factors that drive the global distribution of these PARAFAC components. The explained variance for the humic‐like components was substantially larger (> 70%) than for the amino acid‐like components (< 35%). The environmental variables exhibiting the largest effect on the global distribution of C1 and C2 were apparent oxygen utilisation followed by chlorophyll a. Positive non‐linear relationships between both predictor variables and the two humic‐like PARAFAC components suggest that their distribution are biologically controlled. Compared with the dark ocean (> 200 m), the relationships of C1 and C2 with AOU indicate a higher C1/AOU and C2/AOU ratios of the humic‐like substances in the dark ocean than in the surface ocean where a net effect of photobleaching is also detected. C3 (tryptophan‐like) and C4 (tyrosine‐like) variability was mostly dictated by salinity (S), by means of positive non‐linear relationships, suggesting a primary physical control of their distributions at the global surface ocean scale that could be related to the changing evaporation‐precipitation regime. Remarkably, bacterial biomass (BB) only contributed to explain a minor part of the variability of C1 and C4.

Delta-proteobacterial SAR324 group in hydrothermal plumes on the South Mid-Atlantic Ridge.

In the dark ocean, the SAR324 group of Delta-proteobacteria has been associated with a chemolithotrophic lifestyle. However, their electron transport chain for energy generation and information system has not yet been well characterized. In the present study, four SAR324 draft genomes were extracted from metagenomes sampled from hydrothermal plumes in the South Mid-Atlantic Ridge. We describe novel electron transport chain components in the SAR324 group, particularly the alternative complex III, which is involved in energy generation. Moreover, we propose that the C-type cytochrome, for example the C553, may play a novel role in electron transfer, adding to our knowledge regarding the energy generation process in the SAR324 cluster. The central carbon metabolism in the described SAR324 genomes exhibits several new features other than methanotrophy e.g. aromatic compound degradation. This suggests that methane oxidation may not be the main central carbon metabolism component in SAR324 cluster bacteria. The reductive acetyl-CoA pathway may potentially be essential in carbon fixation due to the absence of components from the Calvin-Benson cycle. Our study provides insight into the role of recombination events in shaping the genome of the SAR324 group based on a larger number of repeat regions observed, which has been overlooked thus far.

(Re)Possession: at Parish St. Michael, Barbados

(Re)Possessionat Parish St. Michael, Barbados Breauna L. Roach (bio) You sit there, wide open—lopsided streak across your faceand think this time, he won’t get out.His rage is now your rage. You’ve founda way to clutch his violence. Will he still thinkhe is God? Your words are his words: failure, victim,waste. You are done pretending to look whole,but you know he likes to play rough.You know he laughs thunder. You are tiredof trembling at storms. His cruelmeans are yours now. Your nightmareis his. He begs for hands to pinchhimself awake orfor a rest as long as death—a single want which you both share.You drag him alongbeyond the mango trees.Pieces of his plum black bodynow trash on the seaside.You pray, You give me a dark ocean,one beyond any creed;nobody will know.By sunrise, you arestained glass eyes.You are asking: who determinesthe difference between painand peace? You are gleaming.You don’t even recognize yourself. [End Page 613] Breauna L. Roach BREAUNA L. ROACH, a Detroit, MI, native, received the Gwendolyn Brooks Writers Association’s Poetry Prize. She graduated from Florida A&M University and is currently studying for the MFA in creative writing at Emerson College. She is both a Cave Canem and Callaloo Creative Writing Workshop Fellow. Copyright © 2016 Johns Hopkins University Press

Factors influencing nitrification rates and the abundance and transcriptional activity of ammonia‐oxidizing microorganisms in the dark northeast P acific O cean

Pelagic marine Thaumarchaea play a primary role in ammonia oxidation, an integral part of nitrification and the nitrogen cycle. This study examines how physicochemical and biological variables influence rates of nitrification and the distribution, abundance and activity of ammonia oxidizers throughout the dark northeast Pacific Ocean. Nitrification rates are highest near the epipelagic-upper mesopelagic transition and decrease with depth according to a Martin-like power function, suggestive of a coupling to the organic matter flux. In contrast, archaeal and bacterial ammonia monooxygenase (amoA) gene abundance remains fairly constant throughout the upper mesopelagic. Density-based composites reveal nitrification to be highest in the upper pycnocline, within the nitrate:silica and ammonium maxima, while ammonia-oxidizing archaea (AOA) abundances are highest in the lower pycnocline. Water column group A (WCA) and B (WCB) AOA amoA genes are present throughout the dark ocean but have no relationship to nitrification rates. WCA comprise the majority of the AOA community above 200 m and WCB comprise the majority of it below 500 m, largely because WCA abundances decrease precipitously from 200 m to 500 m. WCA and WCB amoA genes are actively transcribed throughout the dark ocean, irrespective of conditions. Thaumarchaeal urease (ureC) genes are also present throughout, implying a widespread capacity for mixotrophy; however, unlike amoA, their expression is not detectable. Together, the results support a strong linkage between organic matter flux and nitrification rates, identify density as an important control over AOA distributions, and suggest that WCA and WCB distributions are influenced by the availability of their preferred substrates in the dark ocean.

Ediacaran sedimentology and paleoecology of Newfoundland reconsidered

Ediacaran fossils of Mistaken Point and other localities in Newfoundland have been reconstructed as denizens of a deep, dark ocean, based on a turbidite interpretation of their sedimentary context. Objections to this view include geochemical indications of fresh water and volcanological and sedimentological evidence that they lived in soils of coastal plains and tidal flats. Two distinct assemblages of these fossils are recognized: a low-diversity Aspidella–Heimalora community on sulfidic grey paleosols (Sulfaquent) and a high diversity Fractofusus–Charniodiscus community on red ferruginous paleosols (Fluvent and Udept). These two assemblages and their paleosols were comparable in habitat with Phanerozoic intertidal salt marsh and coastal woodlands, respectively. Paleosol chemical composition is also evidence that Ediacaran communities of Newfoundland lived in humid, cool temperate paleoclimates, unlike arid paleoclimates of the classical Ediacaran biota of South Australia.

Discovery of symbiotic nitrogen fixation and chemoautotrophy in cold-water corals.

Cold-water corals (CWC) are widely distributed around the world forming extensive reefs at par with tropical coral reefs. They are hotspots of biodiversity and organic matter processing in the world’s deep oceans. Living in the dark they lack photosynthetic symbionts and are therefore considered to depend entirely on the limited flux of organic resources from the surface ocean. While symbiotic relations in tropical corals are known to be key to their survival in oligotrophic conditions, the full metabolic capacity of CWC has yet to be revealed. Here we report isotope tracer evidence for efficient nitrogen recycling, including nitrogen assimilation, regeneration, nitrification and denitrification. Moreover, we also discovered chemoautotrophy and nitrogen fixation in CWC and transfer of fixed nitrogen and inorganic carbon into bulk coral tissue and tissue compounds (fatty acids and amino acids). This unrecognized yet versatile metabolic machinery of CWC conserves precious limiting resources and provides access to new nitrogen and organic carbon resources that may be essential for CWC to survive in the resource-depleted dark ocean.

Inspirations from the scientific discovery of the anammox bacteria: A classic example of how scientific principles can guide discovery and development

Anaerobic ammonium oxidation (anammox) is a relatively new pathway within the N cycle discovered in the late 1990s. This eminent discovery not only modified the classical theory of biological metabolism and matter cycling, but also profoundly influenced our understanding of the energy sources for life. A new member of chemolithoautotrophic microorganisms capable of carbon fixation was found in the vast deep dark ocean. If the discovery of the chemosynthetic ecosystems in the deep-sea hydrothermal vent environments once challenged the old dogma “all living things depend on the sun for growth,” the discovery of anammox bacteria that are widespread in anoxic environments fortifies the victory over this dogma. Anammox bacteria catalyze the oxidization of NH4 + by using NO2 - as the terminal electron acceptor to produce N2. Similar to the denitrifying microorganisms, anammox bacteria play a biogeochemical role of inorganic N removal from the environment. However, unlike heterotrophic denitrifying bacteria, anammox bacteria are chemolithoautotrophs that can generate transmembrane proton motive force, synthesize ATP molecules and further carry out CO2 fixation through metabolic energy harvested from the anammox process. Although anammox bacteria and the subsequently found ammonia-oxidizing archaea (AOA), another very important group of N cycling microorganisms are both chemolithoautotrophs, AOA use ammonia rather than ammonium as the electron donor and O2 as the terminal electron acceptor in their energy metabolism. Therefore, the ecological process of AOA mainly takes place in oxic seawater and sediments, while anammox bacteria are widely distributed in anoxic water and sediments, and even in some typical extreme marine environments such as the deep-sea hydrothermal vents and methane seeps. Studies have shown that the anammox process may be responsible for 30%–70% N2 production in the ocean. In environmental engineering related to nitrogenous wastewater treatment, anammox provides a new technology with low energy consumption, low cost, and high efficiency that can achieve energy saving and emission reduction. However, the discovery of anammox bacteria is actually a hard-won achievement. Early in the 1960s, the possibility of the anammox biogeochemical process was predicted to exist according to some marine geochemical data. Then in the 1970s, the existence of anammox bacteria was further predicted via chemical reaction thermodynamic calculations. However, these microorganisms were not found in subsequent decades. What hindered the discovery of anammox bacteria, an important N cycling microbial group widespread in hypoxic and anoxic environments? What are the factors that finally led to their discovery? What are the inspirations that the analyses of these questions can bring to scientific research? This review article will analyze and elucidate the above questions by presenting the fundamental physiological and ecological characteristics of the marine anammox bacteria and the principles of scientific research.

Abundant bioluminescent sources of low-light intensity in the deep Mediterranean Sea and North Atlantic Ocean

Light plays a critical role in the functioning of the marine environment. In the dark ocean, bioluminescent organisms are the only visually relevant sources of light. Cameras of different sensitivities were used to compare the density of pelagic bioluminescent sources (BL) of different light intensities at a regional scale: the image-intensified charge-coupled device for deep-sea research (ICDeep), an image-intensified silicon intensifier target (ISIT) camera and a silicon intensifier target (SIT) camera. Pelagic ICDeep values were higher than ISIT measurements by a mean factor of 7.6 in the Mediterranean Sea and 3.5 in the Atlantic Ocean. Atlantic ISIT values were higher than SIT values by a mean factor of 4.5. Standardising bioluminescence measurements to the near-seafloor (0–400 m above bottom) layer, BLNSF, a logarithmic decrease with depth was observed from three independent datasets (slopes not significantly different): ISIT (Atlantic, Mediterranean), ICDeep (Mediterranean). Intercepts from ICDeep measurements were higher than ISIT measurements by a factor of 4.4. From these trends, a conversion factor to calculate benthopelagic plankton biomass from near-seafloor BLNSF density was derived. Calibration of the ICDeep enabled calculation of the minimum intensity of source visible to that camera. BLNSF sources of low-light intensity (≥1.4 × 10−7 W m−2) outnumber fourfold sources of greater intensity (>ca. 10−6 W m−2 (λpeak = 470 nm). This reveals a high abundance of low-light bioluminescent sources in the marine environment, with mean pelagic densities of 33.15 sources m−3 (Atlantic) and 6.79 sources m−3 (Mediterranean) between 500 and 1500 m depth.

Ubiquitous healthy diatoms in the deep sea confirm deep carbon injection by the biological pump.

The role of the ocean as a sink for CO2 is partially dependent on the downward transport of phytoplankton cells packaged within fast-sinking particles. However, whether such fast-sinking mechanisms deliver fresh organic carbon down to the deep bathypelagic sea and whether this mechanism is prevalent across the ocean requires confirmation. Here we report the ubiquitous presence of healthy photosynthetic cells, dominated by diatoms, down to 4,000 m in the deep dark ocean. Decay experiments with surface phytoplankton suggested that the large proportion (18%) of healthy photosynthetic cells observed, on average, in the dark ocean, requires transport times from a few days to a few weeks, corresponding to sinking rates (124–732 m d−1) comparable to those of fast-sinking aggregates and faecal pellets. These results confirm the expectation that fast-sinking mechanisms inject fresh organic carbon into the deep sea and that this is a prevalent process operating across the global oligotrophic ocean.

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

AbstractThe 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 325 nm (a325) and the fluorescence quantum yield at 340 nm (Φ340) increased, the spectral slope over the wavelength range 275–295 nm (S275–295) and the ratio of spectral slopes over the ranges 275–295 nm and 350–400 nm (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).

Shifts in the meso- and bathypelagic archaea communities composition during recovery and short-term handling of decompressed deep-sea samples.

Dark ocean microbial communities are actively involved in chemoautotrophic and anaplerotic fixation of bicarbonate. Thus, aphotic pelagic realm of the ocean might represent a significant sink of CO2 and source of primary production. However, the estimated metabolic activities in the dark ocean are fraught with uncertainties. Typically, deep-sea samples are recovered to the sea surface for downstream processing on deck. Shifts in ambient settings, associated with such treatments, can likely change the metabolic activity and community structure of deep-sea adapted autochthonous microbial populations. To estimate influence of recovery and short-term handling of deep-sea samples, we monitored the succession of bathypelagic microbial community during its 3 days long on deck incubation. We demonstrated that at the end of exposition, the deep-sea archaeal population decreased threefold, whereas the bacterial fraction doubled in size. As revealed by phylogenetic analyses of amoA gene transcripts, dominance of the active ammonium-oxidizing bathypelagic Thaumarchaeota groups shifted over time very fast. These findings demonstrated the simultaneous existence of various 'deep-sea ecotypes', differentially reacting to the sampling and downstream handling. Our study supports the hypothesis that metabolically active members of meso- and bathypelagic Thaumarchaeota possess the habitat-specific distribution, metabolic complexity and genetic divergence at subpopulation level.

MTSAT-1R Visible Imager Point Spread Correction Function, Part I: The Need for, Validation of, and Calibration With

The multifunctional transport satellite (MTSAT)-1R imager was launched in 2005 and is operated by the Japan Meteorological Agency (JMA). A nonlinear behavior in the MTSAT-1R visible sensor response is observed when the instrument is intercalibrated with coincident moderate resolution imaging spectroradiometer (MODIS) ray-matched radiances. Analysis reveals that the nonlinear behavior is not a result of imager navigation, sensor spectral response difference, nor scan pattern. Examination of coincident MTSAT-1R and MTSAT-2 images reveals that MTSAT-1R dark ocean radiances are affected by neighboring bright clouds, whereas large regions of dark ocean radiances are not impacted. Although the IR and visible optical paths are shared, the MTSAT-1R brightness temperatures are not affected. A dust contaminant coating the mirror, which only affects certain wavelengths, may be one explanation. To address the nonlinearity, a pixel point spread function (PSF) correction algorithm is implemented, wherein most of the radiance contribution is from the pixel field of view itself, as well as including a small contribution from all pixels within a radii of several hundred kilometers. The application of the PSF-corrected ~80% of the affected pixel radiances. After application, a near linear response is observed between the coincident MTSAT-1R and Aqua-MODIS ray-matched radiances, and the intercept is now near the predicted space count of zero. The monthly calibration gain noise is reduced by one-third when compared with the non-PSF-corrected gains. The monthly gains are the most erratic during the first two years of operation, and the MTSAT-1R visible sensor is degrading at ~1.9 % decade.

Analysis of Real Ocean Surface Photo Imaging by Using Weighted Least Square Method

This paper is focused on an analysis of the real images of ocean surface, such as dark ocean surface, sunlight effect on ocean surface and reflected by boat, by using two- dimensional weighted least square method (2D-WLSM). We introduced three different factor values to achieve and get the maximum information of the ocean surface which contained some noisy signal. We determine the attributes of the real image using an image tool, then we convert the axes coordinates of the real image in to the pixel coordinates and obtain the pixel information of the real images by the 2D- WLSM, and finally we compare the response factors of the measured values for the different cases. It is shown that the measured pixel response values are very close to the factor values and the errors between them are very small. Compared the error of the traditional LSM with WLSM we used, our method has shown better graphic results and the error are significantly reduced.

Turnover time of fluorescent dissolved organic matter in the dark global ocean.

Marine dissolved organic matter (DOM) is one of the largest reservoirs of reduced carbon on Earth. In the dark ocean (>200 m), most of this carbon is refractory DOM. This refractory DOM, largely produced during microbial mineralization of organic matter, includes humic-like substances generated in situ and detectable by fluorescence spectroscopy. Here we show two ubiquitous humic-like fluorophores with turnover times of 435±41 and 610±55 years, which persist significantly longer than the ~350 years that the dark global ocean takes to renew. In parallel, decay of a tyrosine-like fluorophore with a turnover time of 379±103 years is also detected. We propose the use of DOM fluorescence to study the cycling of resistant DOM that is preserved at centennial timescales and could represent a mechanism of carbon sequestration (humic-like fraction) and the decaying DOM injected into the dark global ocean, where it decreases at centennial timescales (tyrosine-like fraction).

Seafaring in the 21St Century: The Malaspina 2010 Circumnavigation Expedition

Half a millennium ago Spain completed, under the leadership of the Portuguese ­mariner­ Fernao­ de­Magalhaes,­ the­ first­ circumnavigation of the ocean. A quarter of a century later, Alessandro Malaspina, a navy officer­and­scientist,­led­the­first­Spanish­circumnavigation­ with­ scientific­ goals.­ These­ were­to­provide­an­account­of­the­flora,­fauna,­ and natural resources of the Spanish kingdom, which at the time extended from Italy to the Philippines. In December 2010 a new expedition, the Malaspina Circumnavigation Expedition, on the 200 anniversary of Alessandro Malaspina’s death, departed from the same harbor of Cadiz to circumnavigate the planet on a quest to advance our understanding of the ocean. Five­hundred­years­following­the­first­circumnavigation, the question may be raised if old-fashioned seafaring has still much to add to our understanding of the ocean (Laursen 2011). One might think that recent advances in remote sensing and autonomous vehicles have done away with the need to sail the oceans once more. However, I argue that seafaring is still essential to further our understanding of the oceans and that neither one of the key goals of the Malaspina Circumnavigation Expedition would have been met through the use of remote sensing or autonomous vehicles. The­ goals­ of­ the­Malaspina­Circumnavigation Expedition were to provide an assessment of the state of the oceans in 2011 and to explore, using advanced next-generation sequencing tools, the diversity of life in the ocean, with a particular emphasis in the dark ocean (cf. www.expedicionmalaspina.es). In addition, the project aimed at shifting the interactions among Spanish marine research groups from an excessive focus on competition to a balance between competition and cooperation through the demonstration of the­ benefits­ of­ a­ cooperative­ approach­ and,­ in doing so, build critical mass and leadership capacity. Furthermore, it aimed at prompting the interest for marine science by the Spanish­ public­ and­ to­ foster­ scientific­ vocations­ among its youth. The­project­involved­35­Spanish­research­ groups and a total of 28 international partners from a total of 18 nations across the world, with an estimated total of about 400 scientists and a total of 700 persons involved in various capacities, including logistics, outreach, technical, and administrative support.

Global abundance of planktonic heterotrophic protists in the deep ocean.

The dark ocean is one of the largest biomes on Earth, with critical roles in organic matter remineralization and global carbon sequestration. Despite its recognized importance, little is known about some key microbial players, such as the community of heterotrophic protists (HP), which are likely the main consumers of prokaryotic biomass. To investigate this microbial component at a global scale, we determined their abundance and biomass in deepwater column samples from the Malaspina 2010 circumnavigation using a combination of epifluorescence microscopy and flow cytometry. HP were ubiquitously found at all depths investigated down to 4000 m. HP abundances decreased with depth, from an average of 72±19 cells ml(-1) in mesopelagic waters down to 11±1 cells ml(-1) in bathypelagic waters, whereas their total biomass decreased from 280±46 to 50±14 pg C ml(-1). The parameters that better explained the variance of HP abundance were depth and prokaryote abundance, and to lesser extent oxygen concentration. The generally good correlation with prokaryotic abundance suggested active grazing of HP on prokaryotes. On a finer scale, the prokaryote:HP abundance ratio varied at a regional scale, and sites with the highest ratios exhibited a larger contribution of fungi molecular signal. Our study is a step forward towards determining the relationship between HP and their environment, unveiling their importance as players in the dark ocean's microbial food web.

Not of This Earth: Jack the Ripper and the Development of Gothic Whitechapel

Not of This Earth: Jack the Ripper and the Development of Gothic Whitechapel

Accuracy assessment of Terra-MODIS aerosol optical depth retrievals

Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products have been widely used to address environment and climate change subjects with daily global coverage. Aerosol optical depth (AOD) is retrieved by different algorithms based on the pixel surface, determining between land and ocean. MODIS-Terra and Global Aerosol Robotic Network (AERONET) products can be obtained from the Multi-sensor Aerosol Products Sampling System (MAPSS) for coastal regions during 2000-2010. Using data collected from 83 coastal stations worldwide from AERONET from 2000-2010, accuracy assessments are made for coastal aerosol optical depth (AOD) retrieved from MODIS aboard the Terra satellite. AOD retrieved from MODIS at 0.55μm wavelength has been compared With the AERONET derived AOD, because it is reliable with the major wavelength used by many chemistry transport and climate models as well as previous MODIS validation studies. After removing retrievals with quality flags below1 for Ocean algorithm and below 3 for Land algorithm, The accuracy of AOD retrieved from MODIS Dark Target Ocean algorithms (correlation coefficient R2 is 0.844 and a regression equation of τM = 0.91·τA + 0.02 (where subscripts M and A represent MODIS and AERONET respectively), is the greater than the MODIS Dark Target Land algorithms (correlation coefficient R2 is 0.764 and τM = 0.95·τA + 0.03) and the Deep Blue algorithm (correlation coefficient R2 is 0.652 and τM = 0.81·τA + 0.04). The reasons of the retrieval error in AOD are found to be the various underlying surface reflectance. Therefore, the aerosol models and underlying surface reflectance are the dominant factors which influence the accuracy of MODIS retrieval performance. Generally the MODIS Land algorithm implements better than the Ocean algorithm for coastal sites.

Depth-Specific Distribution of the SAR116 Phages Revealed by Virome Binning

HMO-2011, a recently isolated lytic phage that infects the SAR116 bacterial clade, represents one of the most abundant phage types in the oceans. In this study, the HMO-2011 genome sequence was compared with virome sequences obtained from various depths of the Pacific Ocean regions using metagenome binning. HMO-2011 was confirmed to be one of the most highly assigned viruses, with a maximum of 7.6% of total reads assigned. The HMO-2011-type phages demonstrated a depth-specific distribution, showing more abundance in the euphotic zone of coastal, transition, and open ocean regions as compared with the dark ocean.

Analysis of XCO2 retrieval sensitivity using simulated Chinese Carbon Satellite (TanSat) measurements

We present a study on the retrieval sensitivity of the column-averaged dry-air mole fraction of CO2 (XCO2) for the Chinese carbon dioxide observation satellite (TanSat) with a full physical forward model and the optimal estimation technique. The forward model is based on the vector linearized discrete ordinate radiative transfer model (VLIDORT) and considers surface reflectance, gas absorption, and the scattering of air molecules, aerosol particles, and cloud particles. XCO2 retrieval errors from synthetic TanSat measurements show solar zenith angle (SZA), albedo dependence with values varying from 0.3 to 1 ppm for bright land surface in nadir mode and 2 to 8 ppm for dark surfaces like snow. The use of glint mode over dark oceans significantly improves the CO2 information retrieved. The aerosol type and profile are more important than the aerosol optical depth, and underestimation of aerosol plume height will introduce a bias of 1.5 ppm in XCO2. The systematic errors due to radiometric calibration are also estimated using a forward model simulation approach.