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Response function of the objective analysis scheme as a function of wavelength for WOA18 and earlier analyses. Response function is normalized to 1.0.
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This atlas consists of a description of data analysis procedures and horizontal maps of climatological distribution fields of temperature at selected standard depth levels of the World Ocean on one-degree and quarter-degree latitude-longitude grids. The aim of the maps is to illustrate large-scale characteristics of the distribution of ocean temper...
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Context 1
... response functions for the analyses presented in these atlases are given in Table 5 and Figure 2. For comparison purposes, the response function used by Levitus (1982), WOA94, and others are also presented. ...Context 2
... advantage of the analysis techniques used in this atlas is that we know the amount of smoothing by objective analyses as given by the response function in Table 5 and Figure 2. We believe this to be an important function for constructing and describing a climatology of any geophysical parameter. Particularly when computing anomalies from a standard climatology, it is important that the synoptic field be smoothed to the same extent as the climatology, to prevent generation of spurious anomalies simply through differences in smoothing. ...Similar publications
Recently, many remote-sensing (RS) based datasets providing features of individual fire events from gridded global burned area products have been released. Although very promising, these datasets still lack a quantitative estimate of their accuracy with respect to historical ground-based fire databases. Here, we compared three state-of-the-art RS d...
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... Panel (b) shows pressure and surface wind pattern in boreal winter (right top panel) and in boreal summer (right bottom panel). Average annual surface temperature and surface salinity from the World Ocean Atlas 2018 (Boyer et al., 2018) plotted using Ocean Data View (ODV) (Schlitzer, 2023). ITF = Indonesian throughflow; LC = Leeuwin Current; NEC = North Equatorial Current; SEC = South Equatorial Current; EUC = Equatorial Undercurrent; CC = California Current. 4 of 28 summer, due to the low pressure over the Pilbara in northwest Australia, where local insolation heats the land, wind originating from the north-west as a part of south Asian monsoon, brings moisture from the Indian Ocean to northwest Australia, leading to high precipitation and increased riverine sediment load into the ocean (Chang et al., 2006;Suppiah, 1992). ...
Studying tropical hydroclimate and productivity change in the past is critical for understanding global climate dynamics. Northwest Australia is an ideal location for investigating Australian monsoon dynamics, the variability of the Indonesian Throughflow (ITF), and their impact on past productivity and Pacific warm pool evolution, which remain poorly understood during the 40 kyr world in the mid‐early Pleistocene. In this study, we present multi‐proxy records from International Ocean Discovery Program (IODP) Site U1483 in the Timor Sea spanning the last 2,000 ka, including orbitally‐resolved records from the 40 kyr world between 2,000 and 1,300 ka. Our results suggest that northwest Australia underwent a step of increased aridification and that productivity in the Timor Sea declined during the transition from ∼1,700 to ∼1,400 ka. We attribute this aridification to the reduced moisture supply to this region caused by the ITF restriction and warm pool contraction. We ascribe the declined productivity to a decrease in the nutrient supply of the Pacific source water associated with global nutrient redistribution. At orbital timescale, multiple mechanisms, including sea level changes, monsoon, and the Intertropical Convergence Zone (ITCZ) dynamics, and variations in the ITF and Walker circulation could have controlled variations of productivity and terrigenous input in the Timor Sea during the 40 kyr world. Our bulk nitrogen and benthic carbon isotope records suggest a strong coupling to biogeochemical changes in the Pacific during this period. This research contributes to a better understanding of tropical hydroclimate and productivity changes during the 40 kyr world.
... The sites are located at water depths of 1,015 m and 489 m and from here on are referred to as the deep site and the shallow site from the Chilean margin, respectively. The present-day annual mean SST in the study area is 13°C with a seasonal amplitude of 1.4°C (Locarnini et al., 2019). The location is near to the river mouths of the Río Bio-Bio and Río Itata river ...
... The modern seasonal temperature range at this location is 20.9-28.2°C with an annual mean SST of 24.8°C (Locarnini et al., 2019). ...
... We then obtained depth-weighted temperature signals from modern ocean temperatures (Locarnini et al., 2019) and calculated the modelled temperature (T model ) according to Equation 10. We also assume constant and continued settling of particles to the sediment floor throughout the year. ...
The TEX86 paleothermometer has been extensively used to reconstruct past sea water temperatures, but it remains unclear which export depths the proxy represents. Here we used a novel approach to better constrain the proxy recording depths by investigating paleotemperature proxies (TEX86, U37K′ , RI−OH and RI−OH′) from two pairs of proximal (<12 km apart) cores from Chilean and Angola margins, respectively. These cores are from steep continental slopes and lower shelves, which leads to a substantial difference in water depth between them despite being closely located. Surprisingly, the deep and the shallow U37K′ records at the Chilean margin show dissimilarities, in contrast to the similar records from the Angola margin, which may be due to post‐depositional alteration at the former sites. In contrast, the TEX86 records were statistically indistinguishable between the sites at both the locations, even though the GDGT [2]/[3] ratio suggests GDGTs derived from potentially different archaeal communities residing at different depths. A short‐lived difference between the TEX86 records is observed during the last glacial period at the Angola margin, possibly due to a contribution of Antarctic Intermediate Waters to the deep site. Modelling suggests that the TEX86 source signal at our core sites reaches its peak abundance at water depths shallower than 350 m. The RI−OH and RI−OH′ records show similar variability as the TEX86 records, although regional differences in their absolute temperature estimates exist. Our approach using proximal sediment cores at steep slopes appears useful to constrain the export depth of organic proxy signals for paleo‐reconstructions.
... (b) Meridional velocity profile (colors) and density profile (solid line) used as initial and boundary conditions for the model. The velocity profile is based on observations bySchott et al. (2005), and the density profile on the climatological mean (dashed line)(Boyer et al., 2018). ...
Density staircases are observed in an idealized model of a deep western boundary current upon crossing the equator. We propose that the staircases are generated by the excitement of symmetric instability as the current crosses the equator. The latitude at which symmetric instability is excited can be predicted using simple scaling arguments. Symmetric instability generates overturning cells which, in turn, cause the inhomogenous mixing of waters with different densities. The mixing barriers and well mixed regions in density profiles coincide, respectively, with the boundaries and centers of the overturning cells generated by the symmetric instability. This new mechanism for producing density staircases may require us to re‐evaluate the origins of some of the density staircases observed in the Tropical Atlantic.
The Great Barrier Reef is the largest reef system in the modern ocean. To date, the influence of temperature on the origin and long-term evolution of the Great Barrier Reef remains enigmatic. Here, we present a 900–thousand year TEX 86 H -derived temperature proxy record from Ocean Drilling Program Site 820 in the Coral Sea. It demonstrates that the onset of reef growth on the outer shelf was preceded by a rise in summer temperature from ~26° to ~28°C at around 700 thousand years ago (marine isotope stage 17). This approximately 2°C rise in summer sea surface temperatures (SSTs) likely resulted in higher carbonate production rates, which were crucial for the formation of the Great Barrier Reef. Subsequently, reconstructed SSTs remained sufficiently warm for the Great Barrier Reef to thrive and evolve continuously. The evolution of the Great Barrier Reef, therefore, appears to be closely linked to SSTs.
Modern naval warfare environment is becoming increasingly complex, with acoustic-based torpedoes being the most significant threat to submarines. It is essential to develop advanced technologies to enhance submarine survival rates. In this paper, we propose a hierarchical multi-agent reinforcement learning scheme and a realistic underwater simulation environment for optimal submarine torpedo countermeasures and evasive manoeuvres. Our hierarchical model consists of high-level and low-level agents. The high-level agent decides on decoy launches, while the low-level agent executes specific torpedo countermeasures and evasive manoeuvres. We implement underwater simulation environment based on a 6-DOF motion model to realistically simulate underwater object movements and use PID control for accurate and stable physics. This database is used for active and passive SONAR detection of torpedoes and submarines, enhancing the realism of the acoustic environment. We designed 4-level metrics to systematically analyze model performance in static and dynamic environments with single and multiple torpedo scenarios. Also, we propose a new training methodology to address delayed and sparse reward problems by considering submarine manoeuvring characteristics. Experimental results show that our proposed hierarchical architecture demonstrates competitive performance, achieving a survival rate of 89.07% even in the most complex dynamic environment. We demonstrate improved submarine torpedo countermeasures and evasive manoeuvre performance through stable training in complex underwater environments.
Calcium carbonate (CaCO3) dissolution is an integral part of the ocean's carbon cycle. However, laboratory measurements and ocean alkalinity budgets disagree on the rate and loci of dissolution. In situ dissolution studies can help to bridge this gap, but so far published studies have not been utilized as a whole because they have not previously been compiled into one data set and lack carbonate system data to compare between studies. Here, we compile all published measurements of CaCO3 dissolution rates in the water column (11 studies, 752 data points). Combining World Ocean Atlas data (temperature, salinity) with the neural network CANYON‐B (carbonate system variables), we estimate seawater saturation state (Ω) for each rate measurement. We find that dissolution rates at the same Ω vary by 2 orders of magnitude. Using a machine learning approach, we show that while Ω is the main driver of dissolution rate, most variability can be attributed to differences in experimental design, above all bias due to (diffusive) transport and the synthetic or biogenic nature of CaCO3. The compiled data set supports previous findings of a change in the mechanism driving dissolution at Ωcrit = 0.8 that separates two distinct dissolution regimes: rslow = 0.29 · (1 − Ω)0.68(±0.16) mass% day⁻¹ and rfast = 2.95 · (1 − Ω)2.2(±0.2) mass% day⁻¹. Above the saturation horizon, one study shows significant dissolution that cannot solely be explained by established theories such as zooplankton grazing and organic matter degradation. This suggests that other, non‐biological factors may play a role in shallow dissolution.
Based on SAR remote sensing observation and theoretical calculation, the ISWs in the Arctic Kara Sea is studied. A total of 320 Sentinel-1 SAR remote sensing images between July and October 2022 were processed. Among these images, 834 ISWs were identified in 97 remote sensing images. The spatial distribution and propagation patterns of ISWs in the Kara Sea were interpreted. ISWs are widely present in the region east of Novaya Zemlya in the Kara Sea with water depth exceeding 100 m. Different months exhibit distinct spatial characteristics of ISWs in the Kara Sea. The primary reason for the generation of ISWs is the forcing because of the interaction of the tide currents with the intricate topography. And the ocean currents also play a role in regulating ISWs in the Kara Sea. The propagation of ISWs in the Kara Sea is closely associated with the tidal transport process. The amplitudes of ISWs in the Kara Sea was analyzed using the KdV theory and the eKdV theory. The analysis indicates that amplitudes of ISWs between 10m and 19.9 m account for 67% and 29%, respectively. The maximum amplitudes obtained were 41.3 m and 64.5 m. Comparing the theoretical results with in-situ data, it was observed that the amplitudes of ISWs inverted by eKdV theory is closer agreement with the CTD measurement results.
Animal-borne tags are effective instruments for collecting ocean data and can be used to fill spatial gaps in the observing network. We deployed the first conductivity, temperature, and depth (CTD) satellite tags on the dorsal fin of salmon sharks (Lamna ditropis) to demonstrate the potential of sharks to monitor essential ocean variables and oceanographic features in the Gulf of Alaska. Over 1360 km and 36 days in the summer of 2015, the salmon shark collected 56 geolocated, temperature-salinity profiles. The shark swam through a plume of anomalously salty water that originated from the “Blob” and encountered several mesoscale eddies, whose subsurface properties were altered by the marine heatwave. We demonstrate that salmon sharks have the potential to serve as submesoscale-resolving oceanographic platforms and substantially increase the spatial coverage of observations in the Gulf of Alaska.
We examined the changes in the ocean’s upper layer structure involved in the formation of the subtropical mode water in the South Atlantic. Here we present the results from a survey done in the region of formation between 37°W and 32°W and 34°S and 37°S from July–October 2018, using high‐resolution measurements obtained from an underwater glider. From its records, the mode water development was observed for the first time in the South Atlantic as localized chimney‐like patterns in the temperature, salinity, and potential vorticity (PV) measurements with a horizontal scale of (7 ± 2) km, associated with wintertime oceanic convective processes. Over time, these submesoscale structures tend to expand and dominate the region as a large volume of mode water. These vertical structures present highly homogeneous temperature and salinity values. The observed PV was on the order of 5.0 × 10⁻¹¹ m⁻¹ s⁻¹, which is one order of magnitude smaller than the pre‐existent mode water at the lower layers; negative values were observed, indicating active convection. A 1‐D vertical model was used to predict the depth of the mixed layer conditioned by the surface fluxes and triggered by its changes in winter to late spring. Comparisons of the sea surface temperature measured from satellite collocated with the glider’s measurements showed a very good agreement. From this analysis, we were able to establish the decorrelation scales that characterize mode water formation. Further inspection of the glider data yielded temporal decorrelation scales indicative of convection modified by planetary rotation.
