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Sri Lanka, located in the northern Indian Ocean with the Arabian Sea on its western side and the Bay of Bengal on its eastern side and experiences bi-annually reversing monsoon winds. This will explore the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka, particularly along the southern coast, using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The results confirmed the presence of the reversing current system, between the equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the Southwest (SW) monsoon and the westward flowing Northeast Monsoon Current (NMC) during the Northeast (NE) monsoon, respectively. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the south coast. During the SW monsoon, along the west coast, the Island deflects the eastward flowing SMC southward whilst along the east coast the southward flow results from the Sri Lanka Dome (SLD) recirculation. SLD is formed due to SMC interation with the Island. The major upwelling region was located along the south coast due to water convergence and subsequent divergence associated with the offshore transport of water. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind driven flow along the east and west coasts: during the SW (NE) monsoon the flow along the western (eastern) coast was stronger migrating the upwelling centre to the east (west).&nbsp, The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Fifteen papers are included in this PAGEOPH topical issue “Sixty Years of Modern Tsunami Science, Volume 2: Challenges.” The issue starts with a general introduction, and then briefly summarizes all contributions, first papers addressing general topics, and then articles grouped on a regional basis: Northern Pacific, Southeast Pacific, Southwest Pacific and Indonesia, and Mediterranean regions.

An eruption of the Hunga Tonga-hunga Ha’apai Volcanic Eruption on 15 January 2012 caused tsunami waves, observed globally in tide gage records. In this study we investigate the origin of tsunami waves through the analysis of tide gauge records and numerical simulations in the Indo-Pacific region. The atmospheric pressure wave (Lamb wave) due the eruption was recorded in meteorological stations across Australia. The moving pressure jump was recorded as a ~6.5-hPa jump at the Norfolk Island; ~3.5 hPa at Broken Hill, NSW and Perth and was estimated to be travelling at ~340 ms–1. In the deep ocean this allows for Proudman resonance between the ocean and atmosphere generating a meteotsunami propagating westward across the Indian Ocean. Tide gauges located across the whole Indian Ocean basin recorded the meteotsunami generated by the pressure jump. There were two distinct signal on the tide gauge records. The first signal was recorded in advance of the predicted volcanic tsunami along the east coast of Australia and was due to the meteotsunami. The arrival of the second signal corresponded to tsunami wave generated by the displacement of the volcano travelling as a ‘free’ wave. These findings were confirmed by numerical simulations using an ocean circulation model that incorporated a moving atmospheric pressure jump travelling at a speed of ~ 340 ms–1. The long ocean waves were amplified due to Proudman resonance in the deep ocean, where the water was deeper than 5000 m. The model predicted of the meteotsunami corresponded well with observations., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Mesoscale eddies are common physical features in the ocean that are important for the transport of heat and momentum, and for the distribution of biochemical materials in the ocean. The existence of an anomalous, poleward flowing surface current, the Leeuwin Current (LC), drives the highest eddy kinetic energy environment among all the global eastern boundary currents off Western Australia (WA). There is a limitation in comprehensive understanding of spatial and temporal variability, in particular, the formation and vertical structure of mesoscale eddies. Therefore, this study aimed to define the climatology and vertical structure of mesoscale eddies off WA. Eddy characteristics were derived off WA (10‒40ºS, 105‒130ºE) using a vector geometry-based eddy detection algorithm applied to daily satellite altimetry data over the period 1993-2020. The vertical structure of cyclonic eddies (CE) and anti-cyclonic eddies (AE) in the Perth canyon were examined using ocean glider data over the period 2010-2017 obtained from the Australian Integrated Marine Observing System (IMOS). The seasonal and inter-annual variability and the lifecycles of mesoscale eddies were documented off WA. Shorter-lived eddy formations (, The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

In the eastern margin of the Indian Ocean, anomalous poleward-flowing Leeuwin Current (LC) interacts with the local circulation and topographic features along its path promoting instabilities and a highly energetic eddy field. Eddies play a major role on transferring physical and biogeochemical properties over a wide range of spatial and temporal scales. In particular, sub-mesoscale eddies (SME) are believed to intensify vertical fluxes and are crucial for energy transport. However, as continuous high spatial and temporal resolution data are essential for SME characterization due to their short lifespans and length scale, they are still poorly understood. Thus, this research aims to analyse the spatiotemporal variability of sub-mesoscale eddies distribution and characteristics as a response of LC dynamics along the Rottnest Continental Shelf (ROT). We applied an eddy detection and tracking algorithm to long-term (2010-2018) surface current observations obtained using High-Frequency Radar. LC interactions with the Capes Current and offshore eddies promoted zones with high horizontal shear that were linked to SME generation regions. Counter-clockwise (AC) and clockwise (C) SME were prevalent at the eastern and western boundaries of the LC, respectively, remaining close to their generation spots with 25-50h lifespans. Most of AC (C) SME were formed in August (September). AC eddies generation hotspots migrated meridionally with season, whilst C eddies were clustered in a preferential location, but migrated counter-clockwise over the seasons. The analysis of the long-time series provided detailed information of the generation and lifespans of sub-meso scale eddies and their variability in time in the study region., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The live version of this SOP is on the Ocean Gliders community in GITHUB. The home repository of this publication is in the Ocean Best Practices Repository. This standard operating procedure (SOP) document for dissolved oxygen (DO) aims to guide the user through the steps necessary to collect good quality dissolved oxygen data using ocean gliders for both real time and post deployment data streams.

A large percentage of global ocean plastic waste enters the northern hemisphere Indian Ocean (NIO). Despite this, it is unclear what happens to buoyant plastics in the NIO. Because the subtropics in the NIO is blocked by landmass, there is no subtropical gyre and no associated subtropical garbage patch in this region. We therefore hypothesise that plastics "beach" and end up on coastlines along the Indian Ocean rim. In this paper, we determine the influence of beaching plastics by applying different beaching conditions to Lagrangian particle tracking simulation results. Our results show that a large amount of plastic likely ends up on coastlines in the NIO, while some crosses the equator into the southern hemisphere Indian Ocean (SIO). In the NIO, the transport of plastics is dominated by seasonally reversing monsoonal currents, which transport plastics back and forth between the Arabian Sea and the Bay of Bengal. All buoyant plastic material in this region beaches within a few years in our simulations. Countries bordering the Bay of Bengal are particularly heavily affected by plastics beaching on coastlines. This is a result of both the large sources of plastic waste in the region, as well as ocean dynamics which concentrate plastics in the Bay of Bengal. During the intermonsoon period following the southwest monsoon season (September, October, November), plastics can cross the equator on the eastern side of the NIO basin into the SIO. Plastics that escape from the NIO into the SIO beach on eastern African coastlines and islands in the SIO or enter the subtropical SIO garbage patch.

Presented at: Coastal Structures Conference 2019, Hannover, Germany, September 30th – October 2nd, 2019

For thousands of years humankind has sought to explore our oceans. Evidence of this early intrigue dates back to 130,000 BCE, but the advent of remotely operated vehicles (ROVs) in the 1950s introduced technology that has had significant impact on ocean exploration. Today, ROVs play a critical role in both military (e.g. retrieving torpedoes and mines) and salvage operations (e.g. locating historic shipwrecks such as the RMS Titanic), and are crucial for oil and gas (O&G) exploration and operations. Industrial ROVs collect millions of observations of our oceans each year, fueling scientific discoveries. Herein, we assembled a group of international ROV experts from both academia and industry to reflect on these discoveries and, more importantly, to identify key questions relating to our oceans that can be supported using industry ROVs. From a long list, we narrowed down to the 10 most important questions in ocean science that we feel can be supported (whole or in part) by increasing access to industry ROVs, and collaborations with the companies that use them. The questions covered opportunity (e.g. what is the resource value of the oceans?) to the impacts of global change (e.g. which marine ecosystems are most sensitive to anthropogenic impact?). Looking ahead, we provide recommendations for how data collected by ROVs can be maximised by higher levels of collaboration between academia and industry, resulting in win-win outcomes. What is clear from this work is that the potential of industrial ROV technology in unravelling the mysteries of our oceans is only just beginning to be realised. This is particularly important as the oceans are subject to increasing impacts from global change and industrial exploitation. The coming decades will represent an important time for scientists to partner with industry that use ROVs in order to make the most of these ‘eyes in the sea’.

Buoyant marine plastic debris has become a serious problem affecting the marine environment. To fully understand the impact of this problem, it is important to understand the dynamics of buoyant debris in the ocean. Buoyant debris accumulates in “garbage patches” in each of the subtropical ocean basins because of Ekman convergence and associated downwelling at subtropical latitudes. However, the precise dynamics of the garbage patches are not well understood. This is especially true in the southern Indian Ocean (SIO), where observations are inconclusive about the existence and numerical models predict inconsistent locations of the SIO garbage patch. In addition, the oceanic and atmospheric dynamics in the SIO are very different from those in the other oceans. The aim of this paper is to determine the dynamics of the SIO garbage patch at different depths and under different transport mechanisms such as ocean surface currents, Stokes drift, and direct wind forcing. To achieve this, we use two types of ocean surface drifters as a proxy for buoyant debris. We derive transport matrices from observed drifter locations and simulate the global accumulation of buoyant debris. Our results indicate that the accumulation of buoyant debris in the SIO is much more sensitive to different transport mechanisms than in the other ocean basins. We relate this sensitivity to the unique oceanic and atmospheric dynamics of the SIO.

While there is no persistent upwelling along the West-Australian (WA) coastline, sporadic upwelling events have been documented primarily in summer. By analyzing comparatively the variability of both Ekman and geostrophic cross-shore transports over a seasonal cycle, we show that the situation is more contrasted. Based on a composite index computed from satellite data over a 15 year period, calibrated with well documented events, we investigate the factors influencing the development of sporadic upwelling in the region. Overall, the occurrence of transient upwelling events lasting 3–10 days varies largely in space and time. Shelf regions at 31.5 and 34°S are favored with up to 12 upwelling days per month during the austral spring/summer. Although being generally favored from September to April, sporadic upwelling events can also occur at any time of the year at certain locations north of 30°S. On average over 1995–2010, the Ningaloo region (22.5°S) cumulates the highest number of upwelling (∼140 days per year) and is characterized by longer events. The intensity of intermittent upwelling is influenced by the upwelling-favorable winds, the characteristics of the Leeuwin Current (e.g., onshore geostrophic flow, mesoscale eddies and meanders, stratification and nitracline) and the local topography. This suggests that short-living nutrient enrichment of variable magnitude may occur at any time of the year at many locations along the WA coast., This research was supported under Australian Research Council's Discovery Project funding scheme (DP1093510) which also supports V.R. acknowledges support from MICINN and FEDER through project ESCOLA (CTM2012-39025-C02-01) while revising this paper. M.F. is supported by the CSIRO Wealth from Oceans Flagship. The authors acknowledge J. Sudre who provided the satellite archives. QuikSCAT and SeaWinds data are produced by Remote Sensing Systems and sponsored by the NASA Ocean Vector Winds Science Team.

A hydrographic survey offshore Ningaloo reef, north-west Australia, in austral autumn 2010 revealed relatively stable subsurface water masses in the region, despite the influence of interannual variability of the Leeuwin Current (LC). The surface water mass seems slightly more variable at seasonal time scale, probably due to various contributions of the geographically distinct source waters of the LC. A subsurface nitrate maximum (~110–230 m), a prominent feature of the Ningaloo area during autumn, was consistently observed within different water masses. Tightly coupled variations of subsurface nitrate and oxygen at small vertical scale suggest it is due to local in situ remineralization of organic matter likely to accumulate along sharp physical interfaces and possibly favored by injections of oxygenated subsurface waters. Offshore, enhanced levels of surface chlorophyll a within the downwelling-favorable LC are associated with deeper mixed layer depth, eroding the shallow source of nutrients. Close to the continental shelf, these nutrients are observed to be efficiently uplifted within the core of quasi-persistent topographically trapped submesoscale cyclonic eddies dominated by nonlinear effects. A wind-driven coastal upwelling event occurred in autumn and was characterized by a relatively deep source (~100–150 m), coinciding with the subsurface maximum of nutrients, thus promoting coastal productivity locally and farther north by alongshore advection within the Ningaloo current., This research was supported under Australian Research Council's Discovery Project funding scheme (DP1093510) which also supports V.R. Microwave OI SST data are produced by Remote Sensing Systems and sponsored by National Oceanographic Partnership Program, the NASA Earth Science Physical Oceanography Program, and the NASA MEASURES DISCOVER Project. Data are available at www.remss.com.