Reclaiming the Past examines the post-antique history of Argos and how the city's archaeological remains have been perceived and experienced since the late eighteenth century by both local residents ...and foreign visitors to the Greek Peloponnese. The first western visitors to Argos—a city continuously inhabited for six millennia—invariably expected to encounter landscapes described in classical texts—yet what they found fell far short of those expectations. At the same time, local meanings attributed to ancient sites reflected an understanding of the past at odds with the supposed expertise of classically educated outsiders.Jonathan M. Hall details how new views of Argos emerged after the Greek War of Independence (1821–1830) with the adoption of national narratives connecting the newly independent kingdom to its ancient Hellenic past. With rising local antiquarianism at the end of the nineteenth century, new tensions surfaced between conserving the city's archaeological heritage and promoting urban development. By carefully assessing the competing knowledge claims between insiders and outsiders over Argos's rich history, Reclaiming the Past addresses pressing questions about who owns the past.
In the eastern Mediterranean Sea, satellites have observed events of spring surface‐chlorophyll increase in the Rhodes Gyre region recurring intermittently. Few in situ biogeochemical data, however, ...exist to confirm their consistency, elucidate their seasonal characteristics, or discriminate among the possible drivers. During the year 2018, an array of BGC‐Argo floats was deployed in the region, collecting the first‐ever annual time series of in situ profiles of biogeochemical parameters in this area. Their observations demonstrated that nitrates, driven by mixed‐layer dynamics, were available at surface from December 2018 onwards and could have sustained phytoplankton growth. Phytoplankton accumulation at the surface was observed by satellite only in March 2019 when the mixed‐layer depth shoaled. These findings confirm that blooms occurring before the start of seasonal stratification are not easily recorded by satellite observations and reaffirm the need to consolidate the BGC‐Argo network to establish time series of the evolution of biogeochemical processes.
Plain Language Summary
The Levantine Sea, the easternmost area of Mediterranean Sea, is considered one of the poorest oceans on the Earth in terms of abundance of phytoplankton, the microscopic organisms that fuel the marine food web. However, historical data and satellite maps of chlorophyll (the pigment that reveals phytoplankton presence in the water) show episodic increases in the concentration of this pigment in the area near the island of Rhodes. To elucidate the characteristics of these events, a set of six robotic instruments (i.e. the BGC‐Argo floats) was deployed in the Levantine Sea in 2018. A BGC‐Argo float is an autonomous, free‐floating instrument that makes oceanic observations over the first 2,000 m of the water column on a regular basis. This article presents an analysis of the data collected by these six robots. They provided the very first annual time series of biogeochemical observations in area, including during winter, when ship and satellite data are hard to collect. Our results reveal the increase in phytoplankton occurring before the start of seasonal stratification, increase that is not easily recorded by satellite observations and reaffirm the need to consolidate the BGC‐Argo network to establish time series of the evolution of biogeochemical processes.
Key Points
BGC‐Argo floats observe nitrate injections in surface Mediterranean waters
Mixed‐layer dynamics sustain phytoplankton persistence all over winter‐very early spring
The Mediterranean BGC‐Argo network provides unique observations that complement ship‐based sampling and satellite monitoring
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The international Argo program, a global observational array of nearly 4 000 autonomous profiling floats initiated in the late 1990s, which measures the water temperature and salinity of the upper 2 ...000 m of the global ocean, has revolutionized oceanography. It has been recognized one of the most successful ocean observation systems in the world. Today, the proposed decade action “OneArgo” for building an integrated global, full-depth, and multidisciplinary ocean observing array for beyond 2020 has been endorsed. In the past two decades since 2002, with more than 500 Argo deployments and 80 operational floats currently, China has become an important partner of the Argo program. Two DACs have been established to process the data reported from all Chinese floats and deliver these data to the GDACs in real time, adhering to the unified quality control procedures proposed by the Argo Data Management Team. Several Argo products have been developed and released, allowing accurate estimations of global ocean warming, sea level change and the hydrological cycle, at interannual to decadal scales. In addition, Deep and BGC-Argo floats have been deployed, and time series observations from these floats have proven to be extremely useful, particularly in the analysis of synoptic-scale to decadal-scale dynamics. The future aim of China Argo is to build and maintain a regional Argo fleet comprising approximately 400 floats in the northwestern Pacific, South China Sea, and Indian Ocean, accounting for 9% of the global fleet, in addition to maintaining 300 Deep Argo floats in the global ocean (25% of the global Deep Argo fleet). A regional BGC-Argo array in the western Pacific also needs to be established and maintained.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A new 11 year (2004–2014) monthly 1° gridded Argo temperature and salinity data set with 49 vertical levels from the surface to 1950 m depth (named BOA‐Argo) is generated for use in ocean research ...and modeling studies. The data set is produced based on refined Barnes successive corrections by adopting flexible response functions based on a series of error analyses to minimize errors induced by nonuniform spatial distribution of Argo observations. These response functions allow BOA‐Argo to capture a greater portion of mesoscale and large‐scale signals while compressing small‐sale and high‐frequency noise relative to the most recent version of the World Ocean Atlas (WOA). BOA‐Argo data set is evaluated against other gridded data sets, such as WOA13, Roemmich‐Argo, Jamestec‐Argo, EN4‐Argo, and IPRC‐Argo in terms of climatology, independent observations, mixed‐layer depth, and so on. Generally, BOA‐Argo compares well with other Argo gridded data sets. The RMSEs and correlation coefficients of compared variables from BOA‐Argo agree most with those from the Roemmich‐Argo. In particular, more mesoscale features are retained in BOA‐Argo than others as compared to satellite sea surface heights. These results indicate that the BOA‐Argo data set is a useful and promising adding to the current Argo data sets. The proposed refined Barnes method is computationally simple and efficient, so that the BOA‐Argo data set can be easily updated to keep pace with tremendous daily increases in the volume of Argo temperature and salinity data.
Key Points
A new gridded Argo data set, BOA‐Argo, is produced using refined Barnes successive corrections
The new data set is comparable or slightly better than other gridded Argo data sets produced using OI or variational analysis
The BOA‐Argo is able to retain more mesoscale features than other gridded Argo data sets
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•Subsurface elevated nitrate was observed inside a cyclonic eddy.•Elevated nitrate and CHL were observed along the edge of an anti-cyclonic eddy.•Submesoscale process likely played significant roles ...in elevating nitrate and CHL.
The vertical delivery of nutrients from deep water into the euphotic zone is one of the major limitations for the ocean primary productivity. In this study, the influence of multi-scale dynamics on the nitrate distribution observed by two BGC-Argo floats around the Kuroshio Extension is investigated. Vertical fluctuations of iso-nitrate surfaces and isopycnals were found to be correlated to the variation of absolute dynamic topography. In the subtropical Northwestern Pacific Ocean, subsurface nitrate concentration was found to be elevated inside a cyclonic mesoscale eddy during summer, while little nitrate was supplied into the surface layer, which was possibly due to the inhibition of seasonal thermocline. On the northern edge of the Kuroshio Extension, elevated euphotic-layer nitrate and surface chlorophyll concentrations were observed along the periphery of an anti-cyclonic eddy. In addition to horizontal advection, upwelling induced by the submesoscale dynamics is suggested to likely play an important role in the enhancements of nitrate and chlorophyll concentrations. The enhanced vertical delivery of nutrients from depth due to submesoscale dynamics has been hypothesized as a significant source for some satellite-observed events of high surface chlorophyll concentration, but direct evidence from in-situ observations is lacking. In this study, the synchronous occurrence of elevated nitrate and chlorophyll concentrations along the periphery of an anti-cyclonic eddy provides an evidence to support this hypothesis to some extent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Stratified oceanic systems are characterized by the presence of a so‐called Deep Chlorophyll a Maximum (DCM) not detectable by ocean color satellites. A DCM can either be a phytoplankton (carbon) ...biomass maximum (Deep Biomass Maximum, DBM), or the consequence of photoacclimation processes (Deep photoAcclimation Maximum, DAM) resulting in the increase of chlorophyll a per phytoplankton carbon. Even though these DCM (further qualified as either DBMs or DAMs) have long been studied, no global‐scale assessment has yet been undertaken and large knowledge gaps still remain in relation to the environmental drivers responsible for their formation and maintenance. In order to investigate their spatial and temporal variability in the open ocean, we use a global data set acquired by more than 500 Biogeochemical‐Argo floats given that DCMs can be detected from the comparative vertical distribution of chlorophyll a concentrations and particulate backscattering coefficients. Our findings show that the seasonal dynamics of the DCMs are clearly region‐dependent. High‐latitude environments are characterized by a low occurrence of intense DBMs, restricted to summer. Meanwhile, oligotrophic regions host permanent DAMs, occasionally replaced by DBMs in summer, while subequatorial waters are characterized by permanent DBMs benefiting from favorable conditions in terms of both light and nutrients. Overall, the appearance and depth of DCMs are primarily driven by light attenuation in the upper layer. Our present assessment of DCM occurrence and of environmental conditions prevailing in their development lay the basis for a better understanding and quantification of their role in carbon budgets (primary production and export).
Key Points
The main characteristics and drivers of Deep Chlorophyll Maxima (DCM) are analyzed from a global BGC‐Argo database
Latitude and season determine the occurrence and characteristics of DCMs
DCMs result from photoacclimation or biomass accumulation, depending on the availability of light and nitrate
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Understanding spatial and temporal dynamics of non‐algal particles in open ocean is of the utmost importance to improve estimations of carbon export and sequestration. These particles covary with ...phytoplankton abundance but also accumulate independently of algal dynamics. The latter likely represents an important fraction of organic carbon, but it is largely overlooked. A possible way to study these particles is via their optical backscattering properties (bbp) and relationship with chlorophyll‐a (Chl). To this aim, we estimate the fraction of bbp associated with the non‐algal particle portion (
bbpk) that does not covary with Chl by using a global Biogeochemical‐Argo data set. We quantify the spatial, temporal, and vertical variability of
bbpk. In the northern productive areas,
bbpk is a small fraction of bbp and shows a clear seasonal cycle. In the Southern Ocean, bkbp is a major fraction of total bbp. In oligotrophic areas,
bbpk has a smooth annual cycle.
Key Points
The background backscattering of non‐algal particles decrease from Northern to Southern Hemispheres at the surface and in the euphotic layer
The background backscattering of NAP has a clear seasonal cycle in the productive areas and a smooth cycle in oligotrophic seas
The spatial, temporal, and vertical variability of background backscattering of NAP has to be taken into account in ocean carbon studies
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•OSSE is done for Indian Ocean (IO) pCO2 using RAMA + OMNI moorings, Bio-Argo floats and SOOP ship-tracks.•pCO2 data from moorings and ship-tracks are tested for air-sea CO2 flux inversions.•The ...maximum CO2 flux uncertainty reduction (UR) with potential pCO2 data is found.•IO-UR with pCO2 data from moorings and ship-tracks are 30% and 62%, respectively.•Ship-track pCO2 is more efficient than the mooring pCO2 data in CO2 flux inversion.
An observing system simulation experiment (OSSE) is conducted to identify potential locations for making surface ocean pCO2 measurements in the Indian Ocean using the Bayesian Inversion method. As of the SOCATv3 release, the pCO2 data is limited in the Indian Ocean. To improve our modeling of this region, we need to identify where and what observation systems would produce the most good or benefit for their cost. The potential benefits of installing pCO2 sensors in the existing RAMA and OMNI moorings of the Indian Ocean, the potential of Bio-Argo floats (with pH measurements), and the implementation of the ship of opportunity program (SOOP) for underway sampling of pCO2 are evaluated. A cost function of dissolved inorganic carbon as a model state vector and CO2 flux mismatch as the source of error is minimized, and the basin-wide CO2 flux uncertainty reduction is estimated for different seasons. The maximum flux uncertainty reduction achievable by installing pCO2 sensors in the existing RAMA and OMNI moorings is limited to 30% during different seasons. One may consider that around 20 Bio-Argos are still the right choice over installing mooring based pCO2 sensors and achieve uncertainty reduction up to 50% with additional benefit of profiling the sub-surface upto 1000–2000 m. However, a single track SOOP has the potential to reduce the uncertainty by approximately 62%. This study identifies vital RAMA and OMNI moorings and SOOP tracks for observing Indian Ocean pCO2.
Plain Language Summary.
Surface ocean partial pressure of CO2 (pCO2) information is vital for estimating sea-to-air CO2 exchanges. This parameter is least available from the Indian Ocean as compared to other global tropical and southern oceans. There has been no effort made so far to measure surface ocean pCO2 in the Indian Ocean with routine monitoring such as by mounting instruments to moorings or by underway sampling via any ship of opportunity program. Therefore there is a considerable demand to start pCO2 observations in the Indian Ocean. However, one key question that emerges is where to deploy pCO2 instruments in the Indian Ocean to learn the most with limited resources. This study addresses this question with inverse modeling techniques. The study finds that the existing moorings of the Indian Ocean are capable of hosting pCO2 sensors, and data from those are useful to reduce the uncertainty in the surface sea-to-air CO2 flux estimation by a quarter magnitude. In contrast, the Bio-Argo floats with pH sensors, and the ship of opportunity underway sampling of pCO2 may benefit from reducing the same up to 50% and 62%, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Accurate estimation of the underwater light field associated with photosynthetically available radiation (PAR) is critical to compute phytoplankton growth rate and net primary production (NPP), and ...to assess photo‐physiological response of phytoplankton, such as changes in cellular pigmentation. However, methods to estimate PAR used in many previous studies lack in accuracy, likely resulting in significant bias in light‐dependent products such as NPP derived from remote sensing, model simulations, or autonomous platforms. Here we propose and validate a new model for more accurate estimation of the subsurface PAR profile which uses chlorophyll concentration as its input. Validation is performed using 1,744 BGC‐Argo profiles of chlorophyll fluorescence that are calibrated with surface satellite‐derived chlorophyll concentration over their lifetime. The independent verification with the float's PAR sensors confirms the accuracy of satellite chlorophyll estimate worldwide and in the Southern Ocean in particular.
Plain Language Summary
In this study, we propose a new model to compute the underwater light field available for phytoplankton growth. The model uses as its inputs the above water radiation (which can be obtained from public databases) and the subsurface distribution of chlorophyll‐a, a pigment shared by all phytoplankton that can be estimated from sensors deployed on robotic platforms and that is used by many ocean ecosystem models. We test the model accuracy using data observed by the light sensors on autonomous profiling floats and find it performs well. The comparison also highlights that estimates of surface chlorophyll concentrations from satellites are unbiased worldwide, in contrast to some published accounts.
Key Points
The model takes into account the vertical change of chlorophyll and improves the estimate of the subsurface photosynthetically available radiation field
The model is applicable to autonomous platforms, ecosystem and biogeochemical models, and ocean color remote sensing
Model comparison with independent in‐situ radiometry confirms that satellite chlorophyll‐a retrievals are unbiased worldwide
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Coccolithophores (calcifying phytoplankton) form extensive blooms in temperate and subpolar oceans as evidenced from ocean‐color satellites. This study examines the potential to detect ...coccolithophore blooms with BioGeoChemical‐Argo (BGC‐Argo) floats, autonomous ocean profilers equipped with bio‐optical and physicochemical sensors. We first matched float data to ocean‐color satellite data of calcite concentration to select floats that sampled coccolithophore blooms. We identified two floats in the Southern Ocean, which measured the particulate beam attenuation coefficient (cp) in addition to two core BGC‐Argo variables, Chlorophyll‐a concentration (Chl‐a) and the particle backscattering coefficient (bbp). We show that coccolithophore blooms can be identified from floats by distinctively high values of (1) the bbp/cp ratio, a proxy for the refractive index of suspended particles, and (2) the bbp/Chl‐a ratio, measurable by any BGC‐Argo float. The latter thus paves the way to global investigations of environmental control of coccolithophore blooms and their role in carbon export.
Plain Language Summary
Coccolithophores are a group of phytoplankton that form an armor of calcite plates. Coccolithophores may form intense blooms which can be identified from space by so‐called ocean‐color satellites, providing global images of the color of the surface ocean. BioGeoChemical‐Argo (BGC‐Argo) floats, robots profiling down to 2,000 m with a variety of physicochemical and bio‐optical sensors, present an increasingly attractive and cost‐effective platform to study phytoplankton blooms and their impact on oceanic biogeochemical cycles. We show that coccolithophore blooms can be detected by BGC‐Argo floats with high confidence, hence providing a new way to study them at the global scale as well as their role in sinking carbon.
Key Points
We matched profiling float trajectories with ocean‐color satellite observations of coccolithophore blooms
Two simple bio‐optical indices permitted successful identification of coccolithophore blooms from floats in the Southern Ocean
A method for identifying coccolithophore blooms at the global scale is proposed using regional thresholds of bio‐optical float measurements
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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