Oceanography Research Papers - Academia.edu (original) (raw)

Global mean sea levels are projected to gradually rise in response to greenhouse warming. However, on shorter time scales, modes of natural climate variability in the Pacific, such as the El Niño–Southern Oscillation (ENSO), can affect... more

Global mean sea levels are projected to gradually rise in response to greenhouse warming. However, on shorter time scales, modes of natural climate variability in the Pacific, such as the El Niño–Southern Oscillation (ENSO), can affect regional sea level variability and extremes, with considerable impacts on coastal ecosystems and island nations. How these shorter-term sea level fluctuations will change in association with a projected increase in extreme El Niño and its atmospheric variability remains unknown. Using present-generation coupled climate models forced with increasing greenhouse gas concentrations and subtracting the effect of global mean sea level rise, we find that climate change will enhance El Niño–related sea level extremes, especially in the tropical southwestern Pacific, where very low sea level events, locally known as Taimasa, are projected to double in occurrence. Additionally, and throughout the tropical Pacific, prolonged interannual sea level in-undations are also found to become more likely with greenhouse warming and increased frequency of extreme La Niña events, thus exacerbating the coastal impacts of the projected global mean sea level rise.

The authors establish the effect of urbanization on precipitation in the Pearl River Delta of China with data from an annual land use map (1988–96) derived from Landsat images and monthly climate data from 16 local meteorological... more

The authors establish the effect of urbanization on precipitation in the Pearl River Delta of China with data from an annual land use map (1988–96) derived from Landsat images and monthly climate data from 16 local meteorological stations. A statistical analysis of the relationship between climate and urban land use in concentric buffers around the stations indicates that there is a causal relationship from temporal and spatial patterns of urbanization to temporal and spatial patterns of precipitation during the dry season. Results suggest an urban precipitation deficit in which urbanization reduces local precipitation. This reduction may be caused by changes in surface hydrology that extend beyond the urban heat island effect and energy-related aerosol emissions.

Climate variability and change are expected to influence the seasonal cycle in North Pacific sub-arctic marine ecosystems. The hypothesis that timing of nesting and productivity of piscivorous seabirds [kittiwakes (Rissa tridactyla and... more

Climate variability and change are expected to influence the seasonal cycle in North Pacific sub-arctic marine ecosystems. The hypothesis that timing of nesting and productivity of piscivorous seabirds [kittiwakes (Rissa tridactyla and Rissa brevirostris) and murres (Uria aalge and Uria lomvia)] at the Pribilof Islands are related to variation in ocean climate as indexed by changes in sea-ice concentrations (SICs)

The continental shelf of Northeast Brazil is a unique geological region, consisting of shallow-water rhodolith beds. However, very little information exists about the complexity of this part of the continental shelf and its biogenic... more

The continental shelf of Northeast Brazil is a unique geological region, consisting of shallow-water rhodolith beds. However, very little information exists about the complexity of this part of the continental shelf and its biogenic sedimentation. The present study analysed the characteristics of rhodoliths (size, shape and structure) and compares these characteristics with the associated sediments (Grain size, biogenic composition and percentage of CaCO3). The study area was located on a sandstone reef area on the inner continental shelf of Northeast Brazil. Our results show that recently dead rhodoliths are the main component of the pebble fraction with mean diameter near to 2 cm. The focal area is characterised by beds of rhodoliths, featuring individuals of all shapes (discoidal, ellipsoidal and spheroidal), with the ellipsoidal shape being the most abundant. The larger rhodoliths exhibited a near spheroidal shape, and their outer growth forms show high branching density (BIV). The associated sediment was predominantly composed of carbonate from marine fauna and flora, and calcareous algae contributed most to the sand fraction of the sediments. Foraminifera and molluscs were the most abundant biogenic fauna associated with the sediment. The grain size of the sediment was mostly medium and coarse carbonate sand. The results illustrate that there are correlations between the morphology of rhodoliths and the associated sediment. The biogenic composition of the sediment (Rhodophyta and Rizopoda) was correlated with different branching densities of rhodoliths (BII and BIV). The distribution of the sediment grain size also correlated with size, shape (diameter and sphericity) and structure (Branching BIII and BIV) of rhodoliths. Therefore, our results highlight that the correlations between associated sediment and diameter of rhodoliths is a reflection of the abiotic conditions, being principally determined by depth and hydrodynamic energy.

Cave diving is one of the most technical and potential dangerous forms of diving done today. It may involve use of multiple tanks, regulators and gas mixtures or rebreathers, in combination with powerful long-range diver propulsion... more

Cave diving is one of the most technical and potential dangerous forms of diving done today. It may involve use of multiple tanks, regulators and gas mixtures or rebreathers, in combination with powerful long-range diver propulsion vehicles, to penetrate thousands of meters into submerged cave systems where direct ascent to the surface in the case of emergencies is impossible. In order to carry out scientific studies under such difficult conditions, individuals must be highly competent and experienced cave divers. In spite of these problems, numerous scientific investigations in the fields of biology, ecology, microbiology, geology, hydrology and archaeology have carried out by cave diving scientists. Exploratory cave divers have provided the initial impetus for this research by exploring and mapping underwater caves.

Extensive areas of methane-derived authigenic carbonate (MDAC) have been mapped in the Irish Sea. In the Irish Sector, 23 seabed mounds associated with the Codling Fault Zone were identified by multi-beam echo sounder mapping. Inspection... more

Extensive areas of methane-derived authigenic carbonate (MDAC) have been mapped in the Irish Sea. In the Irish Sector, 23 seabed mounds associated with the Codling Fault Zone were identified by multi-beam echo sounder mapping. Inspection by ROV-mounted video showed that these mounds are rocky features rising 5–10 m above the normal seabed; sampling showed that they are comprised of quartz grains bound together by carbonate cement, probably MDAC. Two separate locations have been mapped in the UK Sector. At Texel 11, seabed mounds and a 6–8 m high cliff were mapped geophysically (MBES, SSS and seismic profiler surveys). Video surveys showed that both the mounds and the cliff are rocky reefs colonised by a prolific fauna. Samples proved to be carbonate-cemented sediments, and carbon isotope analysis (δ13C −41 to −46% PDB) showed that the cement was MDAC. Similar surveys of the Holden’s Reefs area proved the presence of similar rocky reefs which are also cemented by MDAC. The total area covered by these two MDAC occurrences is estimated to be >500,000 m2. These MDAC occurrences are comparable in nature and formation to the ‘bubbling reefs’ of the Kattegat. As the bubbling reefs are “seabed features formed by leaking gas”, one of the marine habitats identified by the European Commission’s Habitats Directive as being sensitive and worthy of protection, it is suggested that the Irish Sea carbonate reefs should also be considered as special habitats.

The photophores of Meganyctiphanes were investigated with regard to the control of light production and with respect to their role in a hitherto unknown communication system using light flashes which became evident from observation of... more

The photophores of Meganyctiphanes were investigated with regard to the control of light production and with respect to their role in a hitherto unknown communication system using light flashes which became evident from observation of specialised signalling behaviour. To that purpose the light production was recorded during presentation of a range of stimuli delivered to the intact, tethered shrimp. Stimuli used were changes in ambient light, water turbulence, simulated predator approach and light flashes, as well as electric shocks and serotonin injections. Strong negative light gradients, exaggerating the natural sunset signal, reliably elicited light production, the peak of which lasted on average 2 min. In the late phase of this light production, low frequency water oscillations and turbulent flow (assumed intraspecific communication signals at close range) elicited transient increases in light production. Artificial light flashes presented to a group of shrimp evoked a signalling behaviour in which the animal points the light of its photophore beamers (positioned at the ventral side and normally directed downwards) for a fraction of a second at observers within the same depth level. The responses produced by the signalling behaviour indicate a fixed delay with respect to the triggering flash. Electric stimulation of the ventral nerve cord via implanted electrodes resulted in a strong light production with a latency of 160 ms. Injection of serotonin, resulting in haemolymph concentrations of 10–5 M and higher, initiated increasingly strong and increasingly long-lasting continuous light production. Implications for the control of the photophores are discussed.