Strong Sea Research Articles

The Composition and Structure of Reef Community at Tho Chu Island (South China Sea) after Ketsana Typhoon

Fringing the reefs of the island Tho Chu explored a quarter century later now reexamined in the Gulf of Thailand of the South China Sea. It was found that most of the reefs of the island were lost after the passage of typhoon “Ketsana” accompanied by heavy rains and strong sea waves higher than 2 meters in October 2009. Because of these natural phenomena, physical destruction of much of the coral communities occurred. Removal of terrigenous sediments from the islands in the water has led to increased sedimentation and loss of almost all the scleractinian family Acroporidae, the main building corals on the reefs of the Indo-Pacific. At present, in places where once there was full-reef community succession is restoring the reef due to the survivors of the typhoon colonies of coral genera Pocillopora and Acropora.

Acidification trends in south Swedish forest soils 1986–2008 — Slow recovery and high sensitivity to sea-salt episodes

Soil water chemistry in forest soils over 20years was studied at nine sites in southern Sweden. The aim was to investigate the recovery from acidification and the influence of strong sea salt episodes that occur in the region. All sites but one showed signs of recovery from acidification along with the reduced sulphur deposition, but the recovery progress was slow and the soil water was in most cases still highly acidic at the end of the period. In several cases the recovery was delayed by episodes of sea salt deposition, leading to transient acidification. The less marked decrease of sulphur concentrations in soil water than of sulphur deposition, highlighted the importance of sulphur adsorption/desorption in the acidification and recovery process. Nitrogen retention capacity was exceeded on one site, leading to nitrate leaching and extremely low pH. Storm fellings on two sites in the end of the period led to effects similar to those of regeneration fellings. It was concluded that the soils in the region are in an early stage of recovery. The future progress of recovery strongly depends on future nitrogen retention of forest soils and the frequency of sea salt episodes.

The 2009 Samoan and 2010 Chilean Tsunamis Recorded on the Pacific Coast of Russia

Two remote tsunamis were recorded on the Pacific coast of Russia: a relatively weak Samoan tsunami of September 29, 2009 and a much stronger Chilean tsunami of February 28, 2010. In the area of the South Kuril Islands, records were obtained using autonomous bottom pressure gauges of the Institute of Marine Geology and Geophysics (IMGG). Additionally, for the oceanic coast of the Kamchatka Peninsula, Paramushir, and Bering Islands we used data transmitted from coastal tide gauges of the Russian Tsunami Warning Service (TWS). The maximum trough-to-crest heights of the Samoan tsunami were about 30–40 cm, and were recorded about 3 h after the first tsunami arrival. The maximum Chilean tsunami trough-to-crest wave heights were 218 cm at Severo-Kurilsk, 187 cm at Tserkovnaya Bay (Shikotan Island), and 140 cm at Khodutka Bay (Kamchatka Peninsula). The time between first and maximum waves reached 4 h. Strong sea level oscillations for both events range for a long time: about 15–17 h. The Samoan tsunami induced high-frequency oscillations; a considerable increase in spectral energy in the tsunami spectrum was observed at periods of 4–20 min. In contrast, the Chilean tsunami induced low-frequency oscillations; the dominant periods were 30–80 min. A probable reason for these differences is the different extensions of the source areas (the Chilean source was much larger than the Samoan source) and the different energy radiation directions from the sources. Local topography resonant effects were the main reason of well-expressed peaks in power spectra in different areas: with a period of 10 min (Khodutka Bay), 19–20 min (Malokurilskaya and Tserkovnaya bays), 29 min (Krabovaya Inlet), and 43 min (Avachinskaya Guba and Nikolskoe).

Seasonal dynamics in an intertidal mudflat: the case of a complex trematode life cycle

Seasonal fluctuations of host densities and environmental factors are common in many ecosystems and have consequences for biotic interactions, such as the transmission of par- asites and pathogens. Here, we investigated seasonal patterns in all host stages associated with the complex life cycle of the intertidal trematode Maritrema novaezealandensis on a mudflat where this parasite's prevalence is known to be high (Lower Portobello Bay, Otago Harbour, New Zealand). The first intermediate snail host Zeacumantus subcarinatus, a key second inter- mediate crustacean host, the amphipod Paracalliope novizealandiae, and definitive bird hosts were included in the study. The density (snails, amphipods), abundance (birds), prevalence, i.e. percentage of infected individuals, and infection intensity (snails, amphipods) of the studied organisms were assessed. Furthermore, temperature was recorded in tide pools, where transmis- sion mainly occurs, over a 1 yr period. Overall, the trematode prevalence in snail hosts was 64.5%, with 88.4% of infected snails harbouring M. novaezealandensis. There was a strong sea- sonal signal in prevalence and infection intensity in second intermediate amphipod hosts, with peaks for both parameters in summer (over 90% infected; infection intensity: 1 to 202 parasites per amphipod). This peak coincided with the highest abundance of definitive bird hosts and of small and still uninfected snails present on the mudflat. Our observations indicate that all of the transmission events necessary to complete the complex life cycle of this parasite primarily occur during warmer months.

Reprint of: Modeling Antarctic ice sheet and climate variations during Marine Isotope Stage 31

Marine Isotope Stage 31 (MIS-31) is one of the major interglacials of the early Pleistocene ~1.08 to 1.06Ma. Data from proximal sediment cores around several sectors of Antarctica indicate strong sea surface warming and ice shelf and sea ice retreat. Benthic deep-sea-core δ18O values at this time are some of the lowest of the Pleistocene, indicating both deep sea warming and reduced global ice volume. A coeval alignment of orbital parameters produces one of the strongest high-latitude summer insolation anomalies of the last several million years. Here we use a 3-D ice sheet-shelf model to simulate the evolution of Antarctic ice sheets through the event, and a global climate model to simulate temperatures and sea ice during peak Antarctic warmth. The ice model predicts nearly complete collapse and subsequent recovery of marine ice in West Antarctica, and the ice and climate model results agree well with proximal sediment core data in the Ross Embayment recovered by the ANDRILL and Cape Roberts drilling projects. The dominant forcing is found to be variations in sub-ice-shelf oceanic melting, with insignificant surface melting of terrestrial ice flanks even during peak warmth. Implications are noted in light of other observations and theories of Pliocene–Pleistocene Antarctic ice sheet variability that do involve surface melt.

Storm surges in the Singapore Strait due to winds in the South China Sea

Among the semi-enclosed basins of the world ocean, the South China Sea (SCS) is unique in its configuration as it lies under the main southwest-northeast pathway of the seasonal monsoons. The northeast (NE) monsoon (November–February) and southwest (SW) monsoon (June–August) dominate the large-scale sea level dynamics of the SCS. Sunda Shelf at the southwest part of SCS tends to amplify Sea Level Anomalies (SLAs) generated by winds over the sea. The entire region, bounded by Gulf of Thailand on the north, Karimata Strait on the south, east cost of Peninsular Malaysia on the west, and break of Sunda Shelf on the east, could experience positive or negative SLAs depending on the wind direction and speed. Strong sea level surges during NE monsoon, if coincide with spring tide, usually lead to coastal floods in the region. To understand the phenomena, we analyzed the wind-driven sea level anomalies focusing on Singapore Strait (SS), laying at the most southwest point of the region. An analysis of Tanjong Pagar tide gauge data in the SS, as well as satellite altimetry and reanalyzed wind in the region, reveals that the wind over central part of SCS is arguably the most important factor determining the observed variability of SLAs at hourly to monthly scales. Climatological SLAs in SS are found to be positive, and of the order of 30 cm during NE monsoon, but negative, and of the order of 20 cm during SW monsoon. The largest anomalies are associated with intensified winds during NE monsoon, with historical highs exceeding 50 cm. At the hourly and daily time-scales, SLA magnitude is correlated with the NE wind speed over central part of SCS with an average time lag of 36–42 h. An exact solution is derived by approximating the elongated SCS shape with one-dimensional two-step channel. The solution is utilized to derive simple model connecting SLAs in SS with the wind speeds over central part of SCS. Due to delay of sea level anomaly in SS with respect to the remote source at SCS, the simplified solutions could be used for storm surge forecast, with a lead time exceeding 1 day.

Intraseasonal-to-Interannual Variability of South Indian Ocean Sea Level and Thermocline: Remote versus Local Forcing

Abstract The relative importance of local versus remote forcing on intraseasonal-to-interannual sea level and thermocline variability of the tropical south Indian Ocean (SIO) is systematically examined by performing a suite of controlled experiments using an ocean general circulation model and a linear ocean model. Particular emphasis is placed on the thermocline ridge of the Indian Ocean (TRIO; 5°–12°S, 50°–80°E). On interannual and seasonal time scales, sea level and thermocline variability within the TRIO region is primarily forced by winds over the Indian Ocean. Interannual variability is largely caused by westward propagating Rossby waves forced by Ekman pumping velocities east of the region. Seasonally, thermocline variability over the TRIO region is induced by a combination of local Ekman pumping and Rossby waves generated by winds from the east. Adjustment of the tropical SIO at both time scales generally follows linear theory and is captured by the first two baroclinic modes. Remote forcing from the Pacific via the oceanic bridge has significant influence on seasonal and interannual thermocline variability in the east basin of the SIO and weak impact on the TRIO region. On intraseasonal time scales, strong sea level and thermocline variability is found in the southeast tropical Indian Ocean, and it primarily arises from oceanic instabilities. In the TRIO region, intraseasonal sea level is relatively weak and results from Indian Ocean wind forcing. Forcing over the Pacific is the major cause for interannual variability of the Indonesian Throughflow (ITF) transport, whereas forcing over the Indian Ocean plays a larger role in determining seasonal and intraseasonal ITF variability.

Modeling Antarctic ice sheet and climate variations during Marine Isotope Stage 31

Marine Isotope Stage 31 (MIS-31) is one of the major interglacials of the early Pleistocene ~1.08 to 1.06Ma. Data from proximal sediment cores around several sectors of Antarctica indicate strong sea surface warming and ice shelf and sea ice retreat. Benthic deep-sea-core δ18O values at this time are some of the lowest of the Pleistocene, indicating both deep sea warming and reduced global ice volume. A coeval alignment of orbital parameters produces one of the strongest high-latitude summer insolation anomalies of the last several million years. Here we use a 3-D ice sheet-shelf model to simulate the evolution of Antarctic ice sheets through the event, and a global climate model to simulate temperatures and sea ice during peak Antarctic warmth. The ice model predicts nearly complete collapse and subsequent recovery of marine ice in West Antarctica, and the ice and climate model results agree well with proximal sediment core data in the Ross Embayment recovered by the ANDRILL and Cape Roberts drilling projects. The dominant forcing is found to be variations in sub-ice-shelf oceanic melting, with insignificant surface melting of terrestrial ice flanks even during peak warmth. Implications are noted in light of other observations and theories of Pliocene–Pleistocene Antarctic ice sheet variability that do involve surface melt.

Typhoon‐induced phytoplankton blooms and primary productivity increase in the western North Pacific subtropical ocean

Using multiple satellite observations and series of numerical experiments, this work systematically studied phytoplankton blooms induced by tropical cyclones in the western North Pacific subtropical ocean (WNPSO) because WNPSO is among the world oceans where most number of intense tropical cyclones are found. All eleven typhoon cases passing the study domain in 2003 were examined in detail. It was observed that only two typhoons (18%) were able to induce phytoplankton blooms (chlorophyll‐a concentration increased from ≦0.1 mg m−3 to 0.4–0.8 mg m−3) and strong sea surface temperature cooling of −2.5 to −6°C. The other nine typhoons, including the most intense tropical cyclone on Earth in 2003 (i.e., supertyphoon Maemi), were not able to induce phytoplankton blooms and the associated sea surface temperature cooling was weak (0 to −1.5°C). Using series of numerical experiments, it was found that the presence of warm ocean eddy can effectively isolate the cold, nutrient‐rich water to be entrained to the surface ocean. Under this situation, even category 5 typhoon Maemi at its peak intensity of 150 kts could not induce phytoplankton bloom in the WNPSO. The weak responses of the other eight typhoons were due to insufficient wind intensity and transit time (caused by relatively small storm size and fast translation speed) in this deep nutricline/mixed layer ocean. As a result, the total annual primary production increase induced by typhoons in the WNPSO was estimated to be ∼3.27 × 1012 g C (0.00327 Pg), equivalent to 0.15% of the global annual anthropogenic CO2 uptake. This suggests that though WNPSO has the highest number and intensity of tropical cyclones among the world oceans, tropical cyclones in the WNPSO have little contribution to enhance biological carbon fixation in the context of global carbon‐climate system.

Ice Adhesion Issues in Renewable Energy Infrastructure

Renewable resources supply only a small fraction of global energy demand. The majority of today’s energy is supplied by fossil fuels. The capacity of fossil fueled facilities to produce power is not as location dependent as renewable energy sources. Many mainstream renewable energy sources like wind, solar, and hydrokinetic must be located where the appropriate natural resources are most abundant. Unfortunately, some of the most energy abundant sites for renewable installations (high winds, strong sea currents) are located where climactic conditions are severe and icing is prevalent. This is significant, as many renewable resources can be substantially or completely incapacitated by icing events. This is not the case for coal, natural gas, or nuclear facilities. As the global proportion of renewable energy infrastructure increases, dealing with icing issues will become more critical. In this paper, the impact of icing on current renewable energy resources is discussed. Renewable resources are categorized based on their icing conditions. Some comparison is made among these categories to explore how different icing conditions may impact potential ice mitigation schemes. It is shown that each of the atmospheric, gas turbine and submarine environments all pose icing challenges that require mostly active, energy-intensive deicing solutions. Such active solutions are those that require significant energy input to be operational and effective (e.g., heaters, shakers, etc.). Also, in the interest of optimizing renewable energy reliability and efficiency, robust and passive systems should be pursued. Passive solutions do not require additional energy input during operation to be effective (e.g., coatings, surface treatments). Such solutions will capitalize on surface-engineering and will be based on adhesion science principles.

Sea breezes drive currents on the inner continental shelf off southwest Western Australia

In southwest Western Australia, strong and persistent sea breezes are common between September and February. We hypothesized that on the inner continental shelf, in the absence of tidal forcing, the depth, magnitude, and lag times of the current speed and direction responses to sea breezes would vary though the water column as a function of the sea breeze intensity. To test this hypothesis, field data were used from four sites were that were in water depths of up to 13 m. Sites were located on the inner continental shelf and were on the open coast and in a semi-enclosed coastal embayment. The dominant spectral peak in currents at all sites indicated that the majority of the spectral energy contained in the currents was due to forcing by sea breezes. Currents were aligned with the local orientation of the shoreline. On a daily basis, the sea breezes resulted in increased current speeds and also changed the current directions through the water column. The correlation between wind–current speeds and directions with depth, and the lag time between the onset of the sea breeze and the response of currents, were dependent on the intensity of the sea breezes. A higher correlation between wind and current speeds occurred during strong sea breezes and was associated with shorter lag times for the response of the bottom currents. The lag times were validated with estimates of the vertical eddy viscosity. Solar heating caused the water column to stratify in summer and the sea breezes overcame this stratification. Sea breezes caused the mixed layer to deepen and the intensity of the stratification was correlated to the strength of the sea breezes. Weak sea breezes of 14 m s−1 caused only slight thermal stratification up to 0.5°C. Apart from these effects on the vertical structure of water column, the sea breezes also influenced transport and mixing in the horizontal dimension. The sea breezes in southwest Western Australia rotated in an anticlockwise direction each day and this rotation was translated into the currents. This current rotation was more prominent in surface currents and in the coastal embayment compared to the open coast.

The Japan Earthquake: Problems of Forecast

The results of registration of the catastrophic earthquake of March 11, 2011, that occurred near Honshu Island (Japan) with the broadband bottom seismograph of the Oceanology Institute, Russian Academy of Sciences on a test bed of the Experimental Design Bureau of Oceanologic Equipment (EDBOE), Russian Academy of Sciences (Moscow) are considered. The specification of the equipment and conditions of the experiment are presented. The records of the earthquake made in EDBOE and those made with a seismograph at the University of Portland (Oregon, United States) are compared, since these registration points are located at identical distances from the epicenter, but the distributions of seismic waves are essentially different. The possible directions of the development of methods and equipment for forecasting strong sea earthquakes and tsunami are examined.

Effects of temperature-induced sea breezes on phosphorus dynamics in a shallow eutrophic lake

Wind gusts often contribute to the internal loading of nutrients in standing waters, but the linkage between the meteorological factors inducing wind gusts and phosphorus (P) dynamics in lakes is unclear. We tested the hypothesis that when atmospheric temperature-induced sea breezes occur, the total P (TP) concentration in a shallow eutrophic lake will be significantly greater than when there were no sea breezes. TP concentrations on days with sea breezes were significantly greater than on breezeless days, indicating that strong sea breezes increase sediment resuspension and that sediment P is supplied to surface water. In this case, water temperature also increased with increasing air temperature, which was significantly higher than on the days with no breezes. The high chlorophyll a and pH values alter the sequentially extracted algal available P fractions of suspended particles, which contained high levels of labile- and residual-P and low levels of NaOH-P. The NaOH-P concentration was lower on the days with sea breezes, indicating that P is released from this fraction. Our study illustrates how rising air temperature induces wind gusts, which are an important mechanism for P dynamics in shallow lakes.

Quantifying the influence of sea ice on ocean microseism using observations from the Bering Sea, Alaska

Microseism is potentially affected by all processes that alter ocean wave heights. Because strong sea ice prevents large ocean waves from forming, sea ice can therefore significantly affect microseism amplitudes. Here we show that this link between sea ice and microseism is not only a robust one but can be quantified. In particular, we show that 75–90% of the variability in microseism power in the Bering Sea can be predicted using a fairly crude model of microseism damping by sea ice. The success of this simple parameterization suggests that an even stronger link can be established between the mechanical strength of sea ice and microseism power, and that microseism can eventually be used to monitor the strength of sea ice, a quantity that is not as easily observed through other means.

Planktonic foraminifera shells record seasonal temperature changes

When planktonic foraminifera calcify, the magnesium to calcium (Mg/Ca) ratios in their shells are sensitive to water temperature. This has enabled paleoceanographers to use Mg/Ca ratios measured from multiple fossil foraminifera shells in sediments as a proxy for average water temperatures in the past. Now Haarmann et al. show that some foraminifera Mg/Ca ratios can also be used to determine seasonal variations in temperature. The authors suggest that because planktonic foraminifera calcify over a period of a few weeks to months, the Mg/Ca ratios in single specimens could capture seasonal temperature variations. They tested this in samples of three different foraminifera species collected off the coast of northwestern Africa, where there is strong seasonal sea surface temperature variability. The researchers found that one of the three species, Globigerinoides ruber (pink), did show strong variations in Mg/Ca that tracked seasonal temperature changes and thus could potentially be used to reconstruct seasonality in the near and distant past. (Paleoceanography, doi:10.1029/2010PA002091, 2011)

Modelling the extreme precipitation event over Madeira Island on 20 February 2010

Abstract. In the morning of the 20 February of 2010 an extreme precipitation event occurred over Madeira Island. This event triggered several flash floods and mudslides in the southern parts of the island, resulting in 42 confirmed deaths, 100 injured, and at least 8 people still missing. These extreme weather conditions were associated to a weather frontal system moving northeastwards embedded in a low pressure area centered in the Azores archipelago. This storm was one in a series of such storms that affected Portugal, Spain, Morocco and the Canary islands causing flooding and strong winds. These storms were bolstered by an unusually strong sea surface temperature gradient across the Atlantic Ocean. In this study, the WRF model is used to evaluate the intensity and predictability of this precipitation extreme event over the island. The synoptic/orographic nature of the precipitation is also evaluated, as well as the sensitivity of the model to horizontal resolution and cumulus parameterization. Orography was found to be the main factor explaining the occurrence, amplitude and phase of precipitation over the Island.

MBAS (Methylene Blue Active Substances) and LAS (Linear Alkylbenzene Sulphonates) in Mediterranean coastal aerosols: Sources and transport processes

Abstract Methylene Blue Active Substances (MBAS) and Linear Alkylbenzene Sulphonates (LAS) concentrations, together with organic carbon and ions were measured in atmospheric coastal aerosols in the NW Mediterranean Basin. Previous studies have suggested that the presence of surfactants in coastal aerosols may result in vegetation damage without specifically detecting or quantifying these surfactants. Coastal aerosols were collected at a remote site (Porquerolles Island-Var, France) and at a more anthropised site (San Rossore National Park-Tuscany, Italy). The chemical data were interpreted according to a comprehensive local meteorological analysis aiming to decipher the airborne source and transport processes of these classes of compounds. The LAS concentration (anthropogenic surfactants) was measured in the samples using LC-MS/MS, a specific analytical method. The values were compared with the MBAS concentration, determined by a non-specific analytical method. At Porquerolles, the MBAS concentration (103 ± 93 ng m −3 ) in the summer samples was significantly higher than in the winter samples. In contrast, LAS concentrations were rarely greater than in the blank filters. At San Rossore, the mean annual MBAS concentration (887 ± 473 ng m −3 in PM10) contributed about 10% to the total atmospheric particulate organic matter. LAS mean concentration in these same aerosol samples was 11.5 ± 10.5 ng m −3 . A similar MBAS (529 ± 454 ng m −3 ) – LAS (7.1 ± 4.1 ng m −3 LAS) ratio of ∼75 was measured in the fine (PM2.5) aerosol fraction. No linear correlation was found between MBAS and LAS concentrations. At San Rossore site the variation of LAS concentrations was studied on a daily basis over a year. The LAS concentrations in the coarse fraction (PM10–2.5) were higher during strong sea storm conditions, characterized by strong air flow coming from the sea sector. These events, occurring with more intensity in winter, promoted the formation of primary marine aerosols containing LAS from the sea surface microlayer. In contrast to LAS, MBAS concentrations in the coarse fraction peaked in summer. Therefore, different sources are suggested for the two classes of compounds. In summer, increased MBAS concentration could be an indicator of phytoplanktonic blows enriching the sea surface microlayer with biogenic surfactants. In winter, some spikes in MBAS concentrations in the coarse fraction could be related to LAS concentrations and sea storm events. Moreover, in the fine fraction MBAS have a large concentration maxima in winter, corresponding to air masses coming from polluted continental areas. It is concluded that MBAS concentration in the fine or the coarse fraction is not an appropriate surrogate measurement of LAS concentration in aerosols because of the significant contribution from other sources to the MBAS concentration.

Field-based validation of a diagenetic effect onG. ruberMg/Ca paleothermometry: Core top results from the Aegean Sea (eastern Mediterranean)

Recent work across the Mediterranean Sea has illustrated the salinity and overgrowth effects on planktonic foraminiferal Mg/Ca, which potentially confound the use of this as a temperature proxy for paleoceanographic reconstructions. To test and verify these effects, we present new Aegean Sea results which reveal Mg/Ca values that were unreasonably high to be explained by temperature or salinity variations alone, confirming that foraminiferal Mg/Ca is affected by diagenesis. We have specifically targeted Globigerinoides ruber (w, sensu stricto), from a series of modern core tops spanning a strong sea surface salinity gradient and a minor sea surface temperature range, along a north-south Aegean Sea transect. Scanning Electron Microscopy analyses show that G. ruber specimens were covered by microscale euhedral crystallites of inorganic precipitates. This secondary calcite phase seems to be responsible for the anomalously high Mg/Ca ratios and likely formed near the sediment/water interface from CaCO3 supersaturated interstitial seawater. We also have clear evidence of diagenetic alteration in a north-south direction along the Aegean Sea, possibly depending on salinity and calcite saturation state gradients. These observations illustrate the necessity of alternative techniques (e.g., flow-through time resolved analysis or laser ablation inductively coupled plasma mass spectrometry) to potentially overcome these diagenetic issues and develop a more reliable and sensitive temperature proxy in similar subtropical settings characterized by high salinity, excessive evaporation, and restricted circulation.

Ocean Preconditioning of Cyclone Nargis in the Bay of Bengal: Interaction between Rossby Waves, Surface Fresh Waters, and Sea Surface Temperatures*

Abstract An in-depth data analysis was conducted to understand the occurrence of a strong sea surface temperature (SST) front in the central Bay of Bengal before the formation of Cyclone Nargis in April 2008. Nargis changed its course after encountering the front and tracked along the front until making landfall. One unique feature of this SST front was its coupling with high sea surface height anomalies (SSHAs), which is unusual for a basin where SST is normally uncorrelated with SSHA. The high SSHAs were associated with downwelling Rossby waves, and the interaction between downwelling and surface fresh waters was a key mechanism to account for the observed SST–SSHA coupling. The near-surface salinity field in the bay is characterized by strong stratification and a pronounced horizontal gradient, with low salinity in the northeast. During the passage of downwelling Rossby waves, freshening of the surface layer was observed when surface velocities were southwestward. Horizontal convergence of freshwater associated with downwelling Rossby waves increased the buoyancy of the upper layer and caused the mixed layer to shoal to within a few meters of the surface. Surface heating trapped in the thin mixed layer caused the fresh layer to warm, whereas the increase in buoyancy from low-salinity waters enhanced the high SSHA associated with Rossby waves. Thus, high SST coincided with high SSHA. The dominant role of salinity in controlling high SSHA suggests that caution should be exercised when computing hurricane heat potential in the bay from SSHA. This situation is different from most tropical oceans, where temperature has the dominant effect on SSHA.

Fractality of eroded coastlines of correlated landscapes

Using numerical simulations of a simple sea-coast mechanical erosion model, we investigate the effect of spatial long-range correlations in the lithology of coastal landscapes on the fractal behavior of the corresponding coastlines. In the model, the resistance of a coast section to erosion depends on the local lithology configuration as well as on the number of neighboring sea sides. For weak sea forces, the sea is trapped by the coastline and the eroding process stops after some time. For strong sea forces erosion is perpetual. The transition between these two regimes takes place at a critical sea force, characterized by a fractal coastline front. For uncorrelated landscapes, we obtain, at the critical value, a fractal dimension D=1.33, which is consistent with the dimension of the accessible external perimeter of the spanning cluster in two-dimensional percolation. For sea forces above the critical value, our results indicate that the coastline is self-affine and belongs to the Kardar-Parisi-Zhang universality class. In the case of landscapes generated with power-law spatial long-range correlations, the coastline fractal dimension changes continuously with the Hurst exponent H, decreasing from D=1.34 to 1.04, for H=0 and 1, respectively. This nonuniversal behavior is compatible with the multitude of fractal dimensions found for real coastlines.