The Hormuz Strait and Makran coastal plains in southeast Iran are significant sources of dust storms in south Asia due to an arid climate with a strong wind regime, low topography, poor vegetation ...cover, and large watersheds with available loose fine-grained sediments. However, their sedimentology, mineralogy, and geomorphic landforms are poorly studied. Granulometry and mineralogy analyses are performed on 46 samples of the coastal plains to explore the influence of aeolian and fluvial processes on the surface sediment properties of the coastal plains. The geomorphic landforms are mapped based on field observations, geological-geomorphological maps, and satellite images. The results show that the main sources of fine-grained dust are distal alluvial fans and flood plains, supratidal plains, and badlands. Calcite, quartz, and feldspar are major, and dolomite and halite are minor minerals. Calcite displays a positive relationship with grain size and eastward subtractive distribution pattern, while quartz exhibits a negative correlation with grain size and eastward additive distribution pattern. Feldspar shows almost a scatter distribution. The monotonous distribution pattern of chlorite, illite, and kaolinite as the main clay minerals is controlled by fluvial and alluvial processes. Aeolian processes influenced the eastward subtractive distribution of montmorillonite and palygorskite as minor clay minerals. The surface sediment texture and mineralogy of the Hormuz Strait coast are strongly affected by northwesterly wind and dust storms. Aeolian processes are dominated on the western Makran coast with large terrestrial and coastal sand dunes, while fluvial and alluvial processes are dominant on the eastern Makran coast with large distal alluvial fans.
•Bering Strait currents vary with the pressure head, local winds, and shelf waves.•E–W shifts of the Aleutian Low alter the Pacific–Arctic oceanic pressure gradient.•The longitude of N. Pacific ...storms drives nearshore divergence in western Alaska.•Polar easterlies drive divergence along north-facing arctic coastlines.•Coastal divergence triggers continental shelf waves in the Bering and Chukchi seas.
We develop a conceptual model of the closely co-dependent Bering shelf, Bering Strait, and Chukchi shelf circulation fields by evaluating the effects of wind stress over the North Pacific and western Arctic using atmospheric reanalyses, current meter observations, satellite-based sea surface height (SSH) measurements, hydrographic profiles, and numerical model integrations. This conceptual model suggests Bering Strait transport anomalies are primarily set by the longitudinal location of the Aleutian Low, which drives oppositely signed anomalies at synoptic and annual time scales. Synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves, whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along-strait (meridional) pressure gradient. In particular, we show that storms centered over the Bering Sea excite continental shelf waves on the eastern Bering shelf that carry northward velocity anomalies northward through Bering Strait and along the Chukchi coast. The integrated effect of these storms tends to decrease the northward Bering Strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the Aleutian Basin and the Western Subarctic Gyre. Ekman suction then increases the water column density through isopycnal uplift, thereby decreasing the dynamic height, sea surface height, and along-strait pressure gradient. Storms displaced eastward over the Gulf of Alaska generate an opposite set of Bering shelf and Aleutian Basin responses. While Ekman pumping controls Canada Basin dynamic heights (Proshutinsky et al., 2002), we do not find evidence for a strong relation between Beaufort Gyre sea surface height variations and the annually averaged Bering Strait throughflow. Over the western Chukchi and East Siberian seas easterly winds promote coastal divergence, which also increases the along-strait pressure head, as well as generates shelf waves that impinge upon Bering Strait from the northwest.
On December 22, 2018, a destructive tsunami related to the phenomena caused by the volcanic eruption of Gunung Anak Krakatau (GAK) was generated following a partial collapse of the volcano that ...caused serious damage and killed more than 400 people. This recent event challenged the traditional understanding of tsunami hazard, warning and response mechanisms and raised the topic of volcanic tsunami hazard. The complex mechanism of this tsunamigenic volcano collapse still needs further investigation as Anak Krakatau is one of the potentially tsunamigenic volcanoes in the world. This study investigates the possible source mechanisms of this phenomenon and their contribution to explaining the observed sea level disturbances by considering the impacts of this destructive event. We configured a flank collapse scenario with a volume of 0.25 km
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as a combination of submarine and subaerial mass movement as the possible source scenarios to the December 22, 2018 Sunda Strait tsunami. A two-layer model is applied to simulate the tsunami generation by these landslides up to 420 s. The tsunami propagation and inundation are then simulated by NAMI DANCE model in GPU environment. The simulation results suggest that this scenario seems capable of generating such a tsunami observed along the coast of Sunda Strait. However, the contribution of the possible submarine mass movements in the close area between GAK and the surrounding islands either to this event or potential tsunami threat in the region is still questionable. We employed a bathymetric dataset through pre- and post-event analyses, which demonstrate submarine slope failures in the southwestern proximity of GAK. Hence, additional two scenarios of elliptical landslide sources on the slopes of bathymetry change area (could be triggered by seismic motion/volcanic eruption) are considered, searching for the possible effects of the tsunami that might be generated by these submarine landslides. The study may also provide some perspective for potential tsunami generation by combined sources and help to elucidate the extent of volcanic tsunami hazard in the region due to potential future eruptions of Gunung Anak Krakatau.
Despite their well‐recognized importance in driving ocean physics and biology, submesoscale (diameter < Rossby radius of deformation) eddies have been extremely difficult to observe due to technical ...difficulties from both field and remote platforms. Here using novel satellite ocean color data products and modified algorithms, we address this challenge for the Florida Straits (22–28°N, 78–85°W). Between 2002 and 2018, while mesoscale eddies (radius >15 km) show strong seasonality with occurrence frequency decreasing from Lower Keys to Upper Keys, submesoscale eddies show little or no seasonality with high occurrence frequency restricted to 30–200‐m isobaths. The number of mesoscale eddies decreases exponentially in size, but submesoscale eddies show a normal distribution in size. These findings are significant in filling our knowledge gap in submesoscale eddies in this physically and ecologically important region as it encompasses world‐renowned coral reefs, seagrasses, and fisheries.
Key Points
Novel satellite imagery enable detection and characterization of submesoscale eddies
The size of submesoscale eddies (radius of 2‐15 km) in the Florida Straits tends to show a normal distribution
There appears an increasing trend in submesoscale eddy occurrence in the Upper Keys of the Florida straits between 2002‐2018
The effect of tides on the Indonesian Throughflow (ITF) is explored in a regional ocean model of South East Asia. Our model simulations, with and without tidal forcing, reveal that tides drive only a ...modest increase in the ITF volume, heat and salt transports toward the Indian Ocean. However, tides drive large regional changes in these transports through Lombok Strait, Ombai Strait and the Timor Sea, and regulate the partitioning of the ITF amongst them. The effect of tidal mixing on the salinity and temperature profiles within the Indonesian Seas drives a small decrease in the heat and salt transports toward the Indian Ocean in all three exit passages. In contrast, the tidal residual circulation due to the interaction between the tides and the topography and stratification (including the effects of tidal mixing on the circulation) leads to a large decrease in the transports toward the Indian Ocean through the Lombok and Ombai straits, but a large increase through the Timor Sea. Hence, the small net contribution from tides to the ITF's volume, heat and salt transports is due to a compensation between large, but opposing tidal residual transports at the combined Lombok and Ombai straits and in the Timor Sea. Our results indicate that explicit representation of tides, often missing in Earth system models, is necessary to accurately capture the ITF's pathway and so the tracer transport from the Pacific into the Indian Ocean.
Plain Language Summary
As part of the general ocean circulation, water from the Pacific Ocean is transported into the Indian Ocean through the Indonesian Seas. This water enters the Indian Ocean through three exit passages: Lombok Strait, Ombai Strait and the Timor Sea. Here, a model that simulates the ocean conditions and circulation in South East Asia is used to explore the role of tides on this transport of water from the Pacific to the Indian Ocean. We found that although tides have a small influence on the total amount of water transferred from the Indonesian Seas into the Indian Ocean, they drive large changes in the relative amount of water that exits through either the Lombok Strait, Ombai Strait or the Timor Sea. Specifically, the interaction between the tides, the topography and the water's vertical density structure within the Indonesian Seas causes tidally‐induced ocean currents that force more water to exit through the Timor Sea, at the expense of less water exiting through the Lombok and Ombai straits. We conclude that the tides regulate the pathway of water exiting into the Indian Ocean through the Indonesian Seas and so may affect the transport of physical, biogeochemical and pollution‐related materials in this region.
Key Points
Currents due to the tides' interaction with topography and stratification drive a modest increase in the Indonesian Throughflow (ITF) transports
Tidal residual circulation drives large but compensatory transports in the three main ITF exit passages
Tides regulate the partitioning of the ITF amongst its three main exit passages into the Indian Ocean
•Summary of early observations and studies of the Arctic Ocean.•The water masses of the Arctic Ocean and their circulation and transformations.•Changes in water mass properties in the Arctic ...Ocean.•The exchanges of volume and freshwater between the Arctic Ocean and the world ocean.
The evolving knowledge of the Arctic Ocean, its hydrography and its water masses and their transformations and circulation is reviewed starting with the observations made on Fram 1893–1896 and extending to the International Polar Year (IPY) 2007–2009. The expeditions and observations after Fram to the mid 20th century as well as the more extensive and systematic studies of water masses and circulation made from ice stations and airborne expeditions from the late 1940s to the late 1970s are briefly described. The early concepts of the connections and exchanges between the Arctic Ocean and the world ocean are also discussed. In the 1980s scientific icebreakers were beginning to enter the inner parts of the Arctic Ocean and large international programmes were launched, culminating in the IPY. The changes in the Arctic Ocean, first noted in the Atlantic layer in 1990 and shortly after in the upper layers, are described. The exchanges between the Arctic Ocean and the surrounding seas through the four main openings, Fram Strait, Barents Sea, Bering Strait and the Canadian Arctic Archipelago as well the volume and freshwater balances of the Arctic Ocean are examined.
Survey data from the northern Bering and Chukchi sea continental shelves in August–September 2012 and 2013 reveal inter-annual differences in the spatial structure of water masses along with ...statistically significant differences in thermohaline properties, chemical properties, and phytoplankton communities. We provide a set of water mass definitions applicable to the northern Bering and Chukchi continental shelves, and we find that the near-bottom Bering-Chukchi Summer Water (BCSW) was more saline in 2012 and Alaskan Coastal Water (ACW) was warmer in 2013. Both of these water masses carried higher nutrient concentrations in 2012, supporting a larger chlorophyll a biomass that was comprised primarily of small (<10µm) size class phytoplankton, so the classical relation between higher nutrient loads and larger phytoplankton does not hold for this region in late summer. The distributions of phytoplankton biomass and size structure reveal linkages between the wind fields, seafloor topography, water mass distributions and the pelagic production. The water mass structure, including the strength and location of stratification and fronts, respectively, differed primarily because of the August regional wind field, which was more energetic in 2012 but was more persistent in direction in 2013. High concentrations of ice in winter and early spring in 2012 and 2013 resembled conditions of the 1980s and early 1990s but the regional ice retreat rate has accelerated in the late 1990s and 2000s so the summer and fall ice concentrations more closely resembled those of the last two decades. Our data show that wind forcing can shut down the Alaskan Coastal Current in the NE Chukchi Sea for periods of weeks to months during the ice-covered winter and during the summer when buoyancy forcing is at its annual maximum. We hypothesize that a decrease in salinity and nutrients from 2012 to 2013 was a consequence of a decreased net Bering Strait transport from 2011 to 2012. Biological ramifications of an accelerated ice melt-back, restructuring of shelf flow pathways, and inter-annually varying Bering Strait nutrient fluxes are mostly unknown but all of these variations are potentially important to the Arctic ecosystem. Our results have implications for the total magnitude and seasonal evolution of primary productivity, secondary production, and the fate of fresh water, heat, and pelagic production on the Bering-Chukchi shelves.
John Askin, a Scots-Irish migrant to North America, built his fur trade between the years 1758 and 1781 in the Great Lakes region of North America. His experience serves as a vista from which to view ...important aspects of the British Empire in North America. The close interrelationship between trade and empire enabled Askin's economic triumphs but also made him vulnerable to the consequences of imperial conflicts and mismanagement. The ephemeral, contested nature of British authority during the 1760s and 1770s created openings for men like Askin to develop a trade of smuggling liquor or to challenge the Hudson's Bay Company's monopoly over the fur trade, and allowed them to boast in front of British officers of having the "Key of Canada" in their pockets. How British officials responded to and even sanctioned such activities demonstrates the vital importance of trade and empire working in concert. Askin's life's work speaks to the collusive nature of the British Empire-its vital need for the North American merchants, officials, and Indigenous communities to establish effective accommodating relationships, transgress boundaries (real or imagined), and reject certain regulations in order to achieve the empire's goals.
Sediments are important hosts for metals and such should be incorporated in aquatic environment monitoring programs. In the present study, the concentrations of metals, multiple geochemical indices ...and guidelines along with multivariate statistical analysis were applied to identify the accumulation, sources and pollution levels of metals in the surface sediment. The mean metal concentrations in the sediments were ranked as follows: Fe > Cr > Ni > V > Zn > Cu > Pb > Cd. Based on the geo-accumulation index and multiple pollution indices the overall pattern of environmental quality status of the khouran Straits were uncontaminated to slightly polluted. Pearson correlation matrix combined with multivariate principal component analysis and cluster analysis suggest that Cd and Pb originated from anthropogenic sources, whereas Fe, Cu, Zn, Ni, V and Cr mostly originated both from natural processes and human activities with predominant anthropogenic influence in the investigated ecosystem.
•Contamination and source identification of metals in sediments of the khouran Straits (Persian Gulf) are studied.•Pollution level in Khouran Straits is uncontaminated to slightly contaminate.•Using multivariate statistical analysis the metals were classified into two main groups according to their sources.•Cd/Pb and other metals emission sources are anthropogenic and anthropogenic (predominant)/lithogenic respectively.
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