Nansen Courses in Environmental Physics

NANCEP 1995 - Alte Briicke, Swakopmund Namibia, November 15 - December 13 199

Watermasses, currents and tides at the Sofala Bank, November 1987

The southern part of the Sofala Bank (in Mozambique) was investigated. A net of closely spaced hydrographic stations were obtained and a current meter mooring consisting of two current meters and a bottom pressure recorder was deployed. High salinity shelf water was observed near shore with a maximum salinity above 36.6 ppt. Both average and tidal currents are discussed. The mean currents are steered by the continental slop and seem to be influenced by the wind. The tides have strong semidiurnal components, with a major axis of 53 cm/s perpendicular to the coast at 60m depth. The possibility that the tides may transport passive drifters with a diurnal vertical migration pattern up to a few kilometers a day is considered

Captura de camarāo de águas pouco profundas e condições ambientais no Banco de Sofala

The present study deals with the performance of shrimp in shallow waters in Sofala Bank presents both seasonal fluctuations as well as fluctuations year to year. These variations may be due to several reasons: abundance of shrimp, fishing effort, fishing techniques and environmental conditions such as the turbidity of the water, tides, temperature and salinity

Generating Levels and Playing Super Mario Bros. with Deep Reinforcement Learning Using various techniques for level generation and Deep Q-Networks for playing

Master's thesis in Information- and communication technology (IKT590)This thesis aims to explore the behavior of two competing reinforcement learning agents in Super Mario Bros. In video games, PCG can be used to assist human game designers by generating a particular aspect of the game. A human game designer can use generated game content as inspiration to build further upon, which saves time and resources. Much research has been conducted on AI in video games, including AI for playing Super Mario Bros. Additionally, there exists a research field focused on PCG for video games, which includes generation of Super Mario Bros. levels. In this thesis, the two fields of research are combined to form a GAN-inspired system of two competing AI agents. One agent is controlling Mario, and this agent represents the discriminator. The other agent generates the level Mario is playing, and represents the generator. In an ordinary GAN system, the generator is attempting to mimic a database containing real data, while the discriminator attempts to distinguish real data samples from the generated data samples. The Mario agent utilizes a DQN algorithm for learning to navigate levels, while the level generator uses a DQN-based algorithm with different types of neural networks. The DQN algorithm utilizes neural networks to predict the expected future reward for each possible action. The expected future rewards are denoted as Q-values. The results show that the generator is capable of generating content better than random when the generator model takes a sequence of tiles as input and produces a sequence of predictions of Q-values as output

Intrusion of warm surface water along the Angolan Namibian Coast in February–March 1995: the 1995 Benguela niño

The upper ocean temperatures in the Angolan-Namibian coastal waters were anomalously high during March 1995, with positive temperature anomalies of up to 8°C. Maximum temperature differences were30–50 m deep, reflecting a deepening of the thermocline from normal depths of 10–30 m. The unusually warm water mass covered the Angolan coast from Cabinda (5°S), the northern limit of the survey area, to atleast 24°S off central Namibia. Higher than normal temperatures were observed as far south as Lüderitz (27°S). Satellite-derived SST and direct observations indicated that the seaward distribution of warm waterextended more than 300 km from the coast. Surface drogues released inshore along the central Namibian shelf suggested a maximum southward extension by 3 March 1995. The warm event was associated withobserved mortalities in sardine Sardinops sagax, horse mackerel Trachurus trachurus capensis and kob Argyrosomus inodorus off the coast. It also caused a southward displacement of sardine stocks from Angola,resulting in an increased availability of pelagic fish in Namibian waters. Conditions have occasionally been anomalously warm in Angolan and Namibian waters in the past, with the last major event in 1984. Theseevents are known as Benguela Niños, because of their resemblance to the well known Pacific El Niño. The 1995 Benguela Niño appeared to be associated with a positive subsurface salinity anomaly of 0.5 × 10–3 inNamibian waters and a negative (-4.0 × 10–3) surface salinity anomaly in Angolan waters, thought to be derived from the freshwater input of the Congo River

Recent changes in the surface salinity of the North Atlantic subpolar gyre

Sea surface salinity (SSS) was measured since 1896 along 60°N between Greenland and the North Sea and since 1993 between Iceland and Newfoundland. Along 60°N away from the shelves, and north of 53°N, the amplitude of the seasonal cycle is comparable to or less than interannual variability. In these parts of the North Atlantic subpolar gyre, large-scale deviations from the seasonal cycle correlate from one season to the next. This suggests that in these regions, summer and autumn surface data are useful for monitoring changes in upper ocean salinity best diagnosed from less common winter surface data. Further south near the subarctic front, the Labrador Current or near shelves where seasonal variability is strong, this is not the case. Along 60°N, the multiannual low-frequency variability is well correlated across the basin and exhibits fresher surface water since the mid 1970s than in the late 1920s to 1960s. SSS in the Irminger Sea along 60°N lags by 1-year SSS farther east in the Iceland Basin. Variability between Iceland and Newfoundland within the Irminger Sea north of 54°N presents similar characteristics to what is observed along 60°N. Variability near the northwest corner of the North Atlantic Current (52°N/45°W) is larger and is not correlated to what is found further north. Maps of SSS were constructed for a few recent seasons between July 1996 and June 2000, which illustrate the fresh conditions found usually during that period across the whole North Atlantic subpolar gyre, although this includes an episode of higher salinity. The SSS anomaly maps have large uncertainties but suggest that the highest SSS occurred before the spring of 1998 in the Iceland Basin, and after that, in the Irminger Sea. This is followed by fresher conditions, first in the Labrador and Iceland Basin, reaching recently the Irminger Sea

The northern Barents Sea: Water mass distribution and modification

The main water masses in the northern Barents Sea are surface water, Arctic water, transformed Atlantic water, and cold bottom water. Using summer data from 1981 and 1982, the formation, distribution, modification and circulation of these water masses are discussed. Recent estimates show that about 2 Sv of Atlantic water enters the Barents Sea by the North Cape Current, balanced by a similar outflow through the strait between Novaya Zemlya and Frans Josef Land. Passing through the Barents Sea, Atlantic-derived water is modified by interaction with other water masses as well as with the atmosphere, and the end products are believed to be important contributors to the hydrographic structure of the Arctic Ocean

Hydrography and circulation in the Filchner Depression, Weddell Sea, Antarctica

Cold and dense Ice Shelf Water (ISW) emerging from the Filchner-Ronne Ice Shelf cavity in the southwestern Weddell Sea flows northward through the Filchner Depression to eventually descend the continental slope and contribute to the formation of bottom water. New ship-born observations of hydrography and currents from Filchner Depression in January 2013 suggest that the northward flow of ISW takes place in a mid-depth jet along the eastern flank of the depression, thus questioning the traditional view with outflow along the western flank. This interpretation of the data is supported by results from a regional numerical model, which shows that ISW flowing northward along the eastern coast of Berkner Island turns eastward and crosses the depression to its eastern side upon reaching the Filchner ice front. The ice front represents a sudden change in the thickness of the water column and thus a potential vorticity barrier. Transport estimates of northward ISW flux based on observations ranges from 0.2-1.0 Sv

Basal melt and freezing rates from first noble gas samples beneath an ice shelf

A climatically‐induced acceleration in ocean‐driven melting of Antarctic ice shelves would have consequences for both the discharge of continental ice into the ocean and thus global sea level, and for the formation of Antarctic Bottom Water and the oceanic meridional overturning circulation. Using a novel gas‐tight in‐situ water sampler, noble gas samples have been collected from six locations beneath the Filchner Ice Shelf, the first such samples from beneath an Antarctic Ice shelf. Helium and neon are uniquely suited as tracers of glacial meltwater in the ocean. Basal meltwater fractions range from 3.6% near the ice shelf base to 0.5% near the sea floor, with distinct regional differences. We estimate an average basal melt rate for the Filchner‐Ronne Ice Shelf of 177 ± 95 Gt/year, independently confirming previous results. We calculate that up to 2.7% of the meltwater has been refrozen, and we identify a local source of crustal helium