Tropical deoxygenation sites revisited to investigate oxygen and nutrient trends

An oxygen decrease of the intermediate-depth low-oxygen zones (300 to 700 m) is seen in time series for selected tropical areas for the period 1960 to 2008 in the eastern tropical Atlantic, the equatorial Pacific and the eastern tropical Indian Ocean. These nearly 5-decade time series were extended to 68 years by including rare historic data starting in 1950 and more recent data. For the extended time series between 1950 and 2018, the deoxygenation trend for the layer 300 to 700 m is similar to the deoxygenation trend seen in the shorter time series. Additionally, temperature, salinity, and nutrient time series in the upper-ocean layer (50 to 300 m) of these areas were investigated since this layer provides critical pelagic habitat for biological communities. Due to the low amount of data available, the results are often not statistically significant within the 95 % confidence interval but nevertheless indicate trends worth discussing. Generally, oxygen is decreasing in the 50 to 300 m layer, except for an area in the eastern tropical South Atlantic. Nutrients also showed long-term trends in the 50 to 300 m layer in all ocean basins and indicate overlying variability related to climate modes. Nitrate increased in all areas. Phosphate also increased in the Atlantic Ocean and Indian Ocean areas, while it decreased in the two areas of the equatorial Pacific Ocean. Silicate decreased in the Atlantic and Pacific areas but increased in the eastern Indian Ocean. Hence, oxygen and nutrients show trends in the tropical oceans, though nutrients trends are more variable between ocean areas than the oxygen trends; therefore, we conclude that those trends are more dependent on local drivers in addition to a global trend. Different positive and negative trends in temperature, salinity, oxygen and nutrients indicate that oxygen and nutrient trends cannot be completely explained by local warming.

A variety of surface waves in ocean-bottom DAS records

<p>Distributed acoustic sensing (DAS) can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recordings over tens of kilometers. Recently, DAS has demonstrated its utility for many seismological applications onshore. However, the use of offshore cables for seismic exploration and monitoring is still in its infancy.<br>In this work, we introduce some new results and observations obtained from a fiber-optic cable offshore the coast of Sanriku, Japan. In particular, we focus on surface wave retrieved from various signals and show that ocean-bottom DAS can be used to extract dispersion curves (DC) over a wide range of frequencies. We show that multi-mode DC can be easily extracted from ambient seismo-acoustic noise cross-correlation functions or F-K analysis. Moderate magnitude earthquakes also contain multiple surface-wave packets that are buried within their coda. Fully-coupled 3-D numerical simulations suggest that these low-amplitude signals originate from the continuous reverberations of the acoustic waves in the ocean layer. </p>

Transport dynamics of pelagic sargassum in the Mexican Caribbean: sensitivity studies to the wind and depth of the transporting ocean layer

<p>The possible fate of pelagic sargassum in the Mexican Caribbean during aug-2018, sep-2018, and apr-2019 is analyzed using a particle-tracking model coupled to diverse datasets of wind [ERA5 reanalysis and the NCEP Climate Forecast System (CFSv2)] and ocean current velocities (HYCOM experiments of high and lower resolution). Advection of particles was computed considering 0, 1, 2, or 3 % of the wind magnitude and either surface currents (0 m) or the averaged currents from the surface to 5 m depth. For each day of the three months, virtual particles were initially located at the vertices of a uniform mesh within the Mexican Caribbean and subsequently tracked for 10 days. Results revealed that the percentage of the wind magnitude accounted for the transport had the greatest impact on the number of particles that ran aground in the Mexican Caribbean: with a higher percentage of the wind magnitude more particles reached the land. The depth of the layer of the ocean currents used in the transport was also important in the results: particle stranding was higher when only surface currents were used. On the other hand, the different data sources had less influence in the results: the simulations using CFSv2 winds resulted in more stranding of particles than those using ERA5 winds, although the differences were relatively small. The number of stranded particles was virtually insensitive to the selection of the ocean data resolution (i. e. HYCOM of high or lower resolution). In general, virtual particles located closer to the coast and further south in the Mexican Caribbean showed the highest probability of running aground on the shores of the Mexican Caribbean. The arrival time depended on the distance from the shore and the wind magnitude. With the wind and current conditions of the three months used for the study, particles located less than 50 km from the shore usually required less than 3 days to run aground. Particles between 50 and 200 km from the shore usually had an arrival time between 3 and 10 days. The dynamics of the particles were similar during each of the months. However, the greatest differences corresponded to apr-2019, when shifting winds and northerlies were observed. This provides an insight of the variations that most likely would result for different months and years. However, sargassum arrivals are expected to occur during the summer, hence these results are relevant for the local preparedness of managing strategies for massive sargassum stranding in the Mexican Caribbean.</p>

A State Space Representation of a Two-Component Energy Balance Model

<p><span>Energy Balance models (EBMs) condense the complicated processes underlying temperature change into a single equation that describes the disequilibrium between absorbed radiation and emitted radiation, where the relation between temperature change and radiative forcing is established. The two-component EBM divides the climate into a mixed shallow ocean/atmosphere layer and a deep ocean layer, thereby accommodating the heat exchange between these two layers. However, the predominant nature of non-stationarity in the observations of climate variables poses challenges for standard statistical inference.</span></p><p><span>This study maps the two-component EBM into a versatile linear state space system (named EBM-SS model) of temperatures in the mixed layer and in the deep ocean layer with radiative forcing. This EBM-SS model allows for the modeling of non-stationarity and time-varying behaviors, the incorporation of multiple alternative variables for one object of interest, and the handling of missing observations. It opens up the possibility to couple with other frameworks to identify the drivers underlying the temperature evolution while maintaining consistency with physical theory. We decompose the latent state of radiative forcing, which is exogenous in this system, into a smooth component and a rough component. The smooth component is modeled as a random walk process with drift to represent the deterministic and stochastic trends of radiative forcing, while the rough component captures the transitory episodes in forcing following major volcanic eruptions.</span></p><p><span>We conduct an empirical analysis on data series at the global level from the period 1955 -- 2019, where the maximum likelihood estimates of the physical parameters are obtained via outputs from the Kalman Filter. We employ proxy variable for the temperature in the deep ocean layer, which is an integral quantity of the ocean temperature and represents the heat storage in the ocean.</span></p>

Oxygen and nutrient trends in the Tropical Oceans

A vertical expansion of the intermediate-depth low-oxygen zones (300 to 700 m) is seen in time series for selected tropical areas for the period 1960 to 2008, in the eastern tropical Atlantic, the equatorial Pacific and the eastern tropical Indian Ocean. These nearly five decade-long time series were extended to 68 years by including rare historic data starting in 1950 and more recent data. For the extended time series between 1950 and 2018 the deoxygenation trend for the layer 300 to 700 m is similar to the deoxygenation trend seen in the shorter time series. Additionally, temperature, salinity and nutrient time series in the upper ocean layer (50 to 300 m) of these areas were investigated since this layer provides critical pelagic habitat for biological communities. Generally, oxygen is decreasing in the 50 to 300 m layer except for an area in the eastern tropical South Atlantic. Nutrients also showed long-term trends in the 50 to 300 m layer in all ocean basins and indicates overlying variability related to climate modes. Nitrate increased in all areas. Phosphate also increased in the Atlantic and Indian Ocean areas, while it decreased in the two areas of the equatorial Pacific Ocean. Silicate decreased in the Atlantic and Pacific areas but increased in the eastern Indian Ocean. Hence oxygen and nutrients show trends in the tropical oceans, though nutrients trends are more variable between ocean areas than the oxygen trends, therefore we conclude that those trends are more dependent on local drivers in addition to a global trend. Different positive and negative trends in temperature, salinity, oxygen and nutrients indicate that oxygen and nutrient trends cannot be completely explained by local warming.

ACOUSTIC NONLINEARITY OF THE UPPER OCEAN LAYER

Представлены результаты исследований нелинейного акустического параметра воды в верхнем слое океана. Метод измерений основан на использовании параметрической генерации звука на различных разностных частотах при бигармоническом излучении высокочастотной накачки. Измерения нелинейного акустического параметра проводились в различные годы в приповерхностном слое в северо-западной части Тихого океана, в верхнем слое до глубины 100 м в Индийском океане, а также на шельфе Японского моря, в бухте Витязь залива Петра Великого. The results of studies of the nonlinear acoustic parameter of water in the upper layer of the ocean are presented. The measurement method is based on the use of parametric sound generation at different difference frequencies under biharmonic radiation of high-frequency pumping. Measurements of the nonlinear acoustic parameter were carried out in various years in the near-surface layer in the North-Western Pacific Ocean, in the upper layer up to a depth of 100 m in the Indian ocean, as well as on the shelf of the Sea of Japan, in the Vityaz Bay of Peter the Great Bay.

EXPEREMENT POLYGON-70

In 1970, an experiment named Polygon–70 was carried out by Russian oceanographers in the tropical zone of the North Atlantic. During this experiment, seventeen autonomous buoy moorings were deployed for the period of half-a-year to measure ocean currents in the ocean layer ranging from the surface to the depth of 1500 m. The outcome of this work was the discovery of what later became known as “synoptic eddies of the open ocean”. It revealed the scale, the nature of time variability and energy of these vortices, as well as an interpretation of the observed phenomena from the point of view of the theory of Rossby waves. It was suggested, that the emergence of the vortices was due to baroclinic instability of large-scale flow. These results of Polygon–70 expedition showed its outstanding value and provided basis for further development of studies of ocean vortices.

Planetary system LHS 1140 revisited with ESPRESSO and TESS

Context. LHS 1140 is an M dwarf known to host two transiting planets at orbital periods of 3.77 and 24.7 days. They were detected with HARPS and Spitzer. The external planet (LHS 1140 b) is a rocky super-Earth that is located in the middle of the habitable zone of this low-mass star. All these properties place this system at the forefront of the habitable exoplanet exploration, and it therefore constitutes a relevant case for further astrobiological studies, including atmospheric observations. Aims. We further characterize this system by improving the physical and orbital properties of the known planets, search for additional planetary-mass components in the system, and explore the possibility of co-orbitals. Methods. We collected 113 new high-precision radial velocity observations with ESPRESSO over a 1.5-yr time span with an average photon-noise precision of 1.07 m s−1. We performed an extensive analysis of the HARPS and ESPRESSO datasets and also analyzed them together with the new TESS photometry. We analyzed the Bayesian evidence of several models with different numbers of planets and orbital configurations. Results. We significantly improve our knowledge of the properties of the known planets LHS 1140 b (Pb ~ 24.7 days) and LHS 1140 c (Pc ~ 3.77 days). We determine new masses with a precision of 6% for LHS 1140 b (6.48 ± 0.46 M⊕) and 9% for LHS 1140 c (mc = 1.78 ± 0.17 M⊕). This reduces the uncertainties relative to previously published values by half. Although both planets have Earth-like bulk compositions, the internal structure analysis suggests that LHS 1140 b might be iron-enriched and LHS 1140 c might be a true Earth twin. In both cases, the water content is compatible to a maximum fraction of 10–12% in mass, which is equivalent to a deep ocean layer of 779 ± 650 km for the habitable-zone planet LHS 1140 b. Our results also provide evidence for a new planet candidate in the system (md = 4.8 ± 1.1M⊕) on a 78.9-day orbital period, which is detected through three independent methods. The analysis also allows us to discard other planets above 0.5 M⊕ for periods shorter than 10 days and above 2 M⊕ for periods up to one year. Finally, our co-orbital analysis discards co-orbital planets in the tadpole and horseshoe configurations of LHS 1140 b down to 1 M⊕ with a 95% confidence level (twice better than with the previous HARPS dataset). Indications for a possible co-orbital signal in LHS 1140 c are detected in both radial velocity (alternatively explained by a high eccentricity) and photometric data (alternatively explained by systematics), however. Conclusions. The new precise measurements of the planet properties of the two transiting planets in LHS 1140 as well as the detection of the planet candidate LHS 1140 d make this system a key target for atmospheric studies of rocky worlds at different stellar irradiations.