Changes In Ocean Environment Research Articles

Terrestrial – Ocean environmental change in the northwestern Pacific from the glacial times to Holocene

The Mixed Water Region (MWR) between the Oyashio Current and the Kuroshio Extension and surrounding terrestrial region have been affected by the global climatic change. The sedimentary core KR02-15 PC6 collected at 40°23.8871′N, 143°29.8663′E in the MWR provides detailed records of pollen and spores and alkenone sea surface temperature (SST) during the last 15 kyr, showing that both ocean and terrestrial environments have been appreciably linked. Abundance of Picea, a proxy for terrestrial cool climate, fluctuated, coinciding with the alkenone-SST change during the interstadial period (15.0–7.7 cal kyr B.P.). Alkenone-SST increased to the modern level at 8.0 cal kyr B.P. and remained almost constant until 2.0 kyr B.P. while the terrestrial warming still continued until 4.0 cal kyr B.P. The rainfall under terrestrial warm condition increased gradually from 7.9 cal kyr B.P. and rapidly from 2.0 cal kyr B.P. Both terrestrial and marine environments cooled down during the last 2 kyr possibly due to the intensified cold Oyashio Current.

Reciprocal Sound Propagation Experiment in Very Shallow Water Area of Hashirimizu Port

A fundamental experiment for environmental monitoring using reciprocal sound propagation was conducted in a very shallow water area in Hashirimizu Port near the entrance to Tokyo Bay. Sound propagation systems with a 12.5 kHz transducer were placed at opposite piers with a distance of about 120 m. Sound travel time was monitored using M-sequence phase-modulated signals so that an accurate arrival time could be detected even in a noisy environment. Arrival time changed throughout the experiment period about 3 weeks almost in accordance with the changes in seawater temperature. However, under certain conditions, such as a low tide and a high negative gradient of the temperature profile in the depth direction, the arrival time was longer than expected. Ray tracing calculation using Bellhop revealed that all rays radiated by the transducer were refracted downward because of the sound speed profile changes. It turns out that the ray path changes depending on ocean environmental changes, especially changes in temperature and the tides. Current speed estimation from reciprocal travel time showed a trend similar to the measurement result of the acoustic doppler current profiler (ADCP). The low reliability of current can be improved by changing the peak tracking method. It also has a potential to get wide area of ocean environment using reflected waves.

The use of fish remains in sediments for the reconstruction of paleoproductivity

The majority of the works concerning fish productivity are based in fish landing records. However, in order to understand the causes of variability in fish productivity (natural and/or anthropogenic) it is essential to have information from periods when human impacts (e.g., fisheries) are considered unimportant. This can be achieved through the use of fish remains, i.e. scales, vertebrae and otoliths, from sediment records. The obtained data can be used to develop time series of fish stocks revealing the history of fish population dynamics over the last centuries or millennia. The majority of these works are located in Eastern Boundary Current Systems (e.g., Benguela, Peru-Humboldt, California), because these are associated with coastal upwelling and high productivity, which in some cases is at the origin of low bottom oxygen levels, leading to scale preservation. A search for fish remains in the Portuguese margin sediments is in progress in the context of the ongoing research project POPEI (High-resolution oceanic paleoproductivity and environmental changes; correlation with fish populations), which intend to fill the gap in studies of this type for the Canary Current System. In this paper we review some general ideas of the use of fish remains, related studies, methodologies and data processing, as well as presenting the first results of POPEI.

MEASUREMENT AND SIMULATION FOR WIND NOISES IN THE OCEAN ENVIRONMENTS WITH NONLINEAR INTERNAL WAVES

This study obtains wind noise variations by experimental data and simulated results to describe meteorological and oceanic effects. The ambient noise data were measured by a vertical line array in the 2001 ASIAEX South China Sea experiment. An acoustic propagation model is used in noise modeling for calculating the sound pressure of noises at receiving sites, including the effects of ocean environmental changes, bottom interactions, and noise fluctuations at different depths. Both range-independent and range-dependent sound speed profiles are generated with in-situ water temperature data. Results show fluctuating noise levels with variations in ocean environments. But the fluctuations are small such that only weak correlation exists in the acoustic noise data and ocean data. Results also indicate that using range-independent sound speed profiles can simulate noise field in range-dependent ocean environments with nonlinear internal waves for shallow regions with flat bottoms.

Interactions between environmental change and shallow water carbonate buildup along the northern Tethyan margin and their impact on the Early Cretaceous carbon isotope record

The evolution of the Early Cretaceous, northern Tethyan carbonate platform was not only influenced by changes in sea level, detrital influx, and surface water temperature but also by changes in trophic levels. We distinguish between phases of carbonate production dominated by oligotrophic photozoan communities and by mesotrophic and eventually colder‐water heterozoan communities. Superimposed on this bimodal trend in platform evolution were phases of platform demise for which we provide improved age control based on ammonite biostratigraphy. The initial phase of these episodes of platform demise corresponds in time to episodes of oceanic anoxic events and environmental change in general. On the basis of a comparison between the temporal changes in an Early Cretaceous, ammonite‐calibratedδ13C record from southeastern France and coeval changes in the platform record, we suggest that the history of carbon fractionation along the northern Tethyan margin was not only influenced by changes in the oceanic carbon cycle such as in the rate of production and preservation of organic and carbonate carbon and in the size of the oceanic dissolved inorganic carbon reservoir, but it was also influenced by the above‐mentioned changes in the ecology and geometry of the adjacent carbonate platform. Phases of photozoan carbonate production induced positive trends in the hemipelagic carbonateδ13C record. Phases of heterozoan carbonate production pushed theδ13C system toward more negative values. Platform drowning episodes implied an initial increase inδ13C values, followed by a longer‐term decrease inδ13C values.

Oceanic environmental changes of subarctic Bering Sea in recent 100 years: Evidence from molecular fossils

The core sample B2-9 from the seafloor of the subarctic Bering Sea was dated with 210Pb to obtain a consecutive sequence of oceanic sedimentary environments at an interval of a decade during 1890—1999. A variety of molecular fossils were detected, including n-alkanes, isoprenoids, fatty acids, sterols, etc. By the characteristics of these fine molecules (C 27 , C 28 , and C 29 sterols) and their molecular indices (Pr/Ph, ∑C + 22 /∑C - 21 , CPI and C18∶2/C18∶0) and in consideration of the variation of organic carbon content, the 100-year evolution history of subarctic sea paleoenvironment was reestablished. It is indicated that during the past 100 years in the Arctic, there were two events of strong climate warming (1920—1950 and 1980—1999), which resulted in an oxidated sediment environment owing to decreasing terrigenous organic matters and increasing marine-derived organic matters, and two events of transitory climate cooling (1910 and 1970—1980), which resulted in a slightly reduced sediment environment owing to increasing terrigenous organic matters and decreasing marine-derived organic matters. It is revealed that the processes of warming/cooling alternated climate are directly related to the Arctic and global climate variations.

Variations of sulfur and carbon isotopes in seawater during the Doushantuo stage in late Neoproterozoic

Successive analyses of sulfur and carbon isotopic compositions of carbonates strata in the Doushantuo Formation in the Yangtze area were accomplished through a method of extracting trace sulfate from carbonates. Sulfur and carbon isotopic compositions of coeval seawater were estimated from the samples that show the least diagenetic alteration. A high-resolution age curve of sulfur isotopes in seawater sulfates was obtained in the Doushantuo stage, which reflects the trend of variation in seawater sulfur isotopes after the Neoproterozoic snowball Earth event. Similar characteristics of variation in carbon isotopes were observed in the coeval carbonates. A large positive δ34S excursion over +20‰ occurs in ancient seawater sulfates in the early Doushantuo stage. Simultaneously, the δ13 C values in ancient seawater carbonates exhibit a positive excursion up to 10‰ The maximum δ34S and δ13C values are +46.4‰ and +6.9‰, respectively. In the middle Doushantuo stage, the range of variation in δ34 S values of seawater is relatively narrow, but δ13C values are quite high. Then, δ34S values of seawater become oscillating, and the same occurs in δ13C values. Negative excursions in δ34 S and δ13 C values occur simultaneously at the end of the Doushantuo stage, and the minimum δ34S and δ13C values dropped down to −10.1‰ and –5.7‰, respectively. The characteristics of variations in the sulfur and carbon isotopes of ancient seawater imply strong changes in oceanic environment that became beneficial to inhabitation and propagation of organism. The organic productivity and burial rate of organic carbon once reached a quite high level during the Doushantuo stage. However, the state of environment became unstable after the global glaciation. The global climate and environment possibly were fluctuating and reiterating. The negative excursions in δ34S and δ13C values occurring at the end of the Doushantuo stage may represent a global event, which might be related to oxidation of deep seawater.

新生代におけるグローバル炭素循環と気候変動との関係―ＣＯ２は長期的気候変動の主要因か？―

Climate change and variations of atmospheric CO2 during Cenozoic have been discussed by many studies. The model results for global carbon cycle and climate change are generally consistent with those of many analytical studies concerning climate events in early Cenozoic, e.g., early Eocene warming events. However, the climate events proposed by analytical studies in late Cenozoic are not wholly inconsistent with the results of the model studies, e.g., Miocene climatic optimum (warming), cooling events in Eocene/Oligocene boundary and middle Miocene (15 Ma). Many problems remain in relation to evaluating CO2 flux by hydrothermal solutions at mid-ocean ridges, island-arc, and back-arc basins in the models. Also, the discrepancy may be derived from errors in estimating weathering flux, organic carbon burial, and change in vegetation. Moreover, another greenhouse effect gas such as methane, land-sea distribution, albedo variations due to the formation of ice-sheets, and temperature distribution attributed to changes in the ocean circulation system should be considered. Recent analytical studies reveal that the CO2 level since Miocene has remained relatively low in spite of the suggested climate events in this period. The mechanism of oceanic environmental change, as well as atmospheric CO2, is especially important to elucidate climate change during Cenozoic.

Terrestrial—oceanic environmental change in the southern Okhotsk sea during the Holocene

The Okhotsk Sea plays a significant role in climatic and oceanic environmental change on regional and global scales. The fluctuation in pollen and spores abundances was investigated in order to reconstruct terrestrial and ocean environmental change during the Holocene. Fluctuation of the total abundance and assemblage of most of pollen and spores reflects terrestrial environmental change along the coastal area of the southern Okhotsk Sea. On the other hand, the abundance of Cryptomeria, Cyclobalanopsis and Castanopsis pollen from plants which are not currently growing in Hokkaido, is suggested to be a good proxy for the intensity of the Tsushima Current. Relatively warm pollen assemblages characterize Periods 1 (calendar age 7240–3050 yr BP) and 3 (150–0 yr BP) while a relatively cold pollen assemblage characterizes Period 2 (3050–150 yr BP). Three warm sub-periods 1a (7240–6500 yr BP), 1c (5900–4550 yr BP) and 1e (4300–3550 yr BP) are associated with relatively strong intensity of the Tsushima Current, transgression, and the occurrence of bivalves living in warm conditions. Continuous cooling started 3000 yr BP. The area remained so cold that the intensified Tsushima Current (2800–2400 and 1700–1400 yr BP) would have made little difference to terrestrial warming in the southern Okhotsk Sea. In the uppermost samples, a large increase in total abundance of pollen and spores may be partly attributed to the modern global warming effect.

Insularity of scientific disciplines and uncertainty about supply: the two keys to the failure of fisheries management

Abstract The roots of the failure of the current system of the management in commercial fisheries, variability of the supply function and interdisciplinary problems are analyzed. Variability in the supply function is linked to our increasing understanding of the importance of the complexity of changes in the ocean environment and human predation on fish stocks. This emphasis on environmental change opens up new approaches to management.

Stable isotope variations in otoliths of Pacific halibut ( Hippoglossus stenolepis) and indications of the possible 1990 regime shift

Stable oxygen and carbon isotope ratios ( δ 18 O and δ 13 C ) from archived otoliths of Pacific halibut, Hippoglossus stenolepis, were measured to examine the most recent regime shifts in British Columbia and the Gulf of Alaska. δ 18 O values of these otoliths ranged from −1.5 to +2.8‰ VPDB, and were consistent with the life stages and migration behavior of halibut. δ 13 C varied from −3.3 to +0.9‰ VPDB, but did not show a transition from the juvenile to the adult stage as does δ 18 O . Evaluation of δ 18 O and δ 13 C values of mature halibut (ages 8–12) indicated that the 1977 regime shift might have a warming impact on the northeast Pacific fish stocks. In contrast, a possible regime shift around 1990 with a bottom seawater temperature decrease of about 2 °C might have occurred in both the areas. The connection between stable isotope variations in otoliths and the climate regime shifts is thus potentially useful in studying the population dynamics of Pacific halibut, and decadal scale (e.g., the last 20–30 years) ocean environmental changes.

Antarctic environmental variability since the late Miocene: ODP Site 745, the East Kerguelen sediment drift

Characterization of sediment from Ocean Drilling Program Site 745, representing the East Kerguelen Ridge sediment drift, addresses important issues surrounding the timing of Miocene to present East Antarctic ice sheet stability and oceanic environmental change. Our results show three periods of greatly enhanced accumulation of Antarctic-derived sediment, at 6.4–5.9 Ma, 4.9–4.4 Ma and 1.1–0.8 Ma, potentially indicative of warmer, less stable ice sheets at these times. Conversely, the accumulation of Antarctic-derived material is comparatively less during the middle of the Pliocene warm epoch (4.8–3.2 Ma). The deep flow forming the Kerguelen drift was stronger during the latest Miocene and earliest Pliocene and has decreased in intensity continuously since then.

Holocene Land–Ocean Interactions and Environmental Change Around the North Sea

Holocene Land–Ocean Interactions and Environmental Change Around the North Sea

Isotopic composition of otoliths as a chemical tracer in population identification of sockeye salmon (Oncorhynchus nerka)

The feasibility of stable oxygen and carbon isotope ratio (δ18O and δ13C) analyses in sagittal otoliths of sockeye salmon (Oncorhynchus nerka) was tested by analyzing the seasonal and annual otolith zones of 44 samples collected from different localities in the northeast Pacific coast. The δ18O and δ13C values of these otoliths ranged from -14.23 to +1.62‰ and from -15.18 to -3.17‰, respectively. The δ18O variations can be divided into two stages from freshwater (-14.2 to -2.5‰) to marine (-2.5 to +1.6‰) that were consistent with the life history of sockeye salmon from juvenile to adult stages. The transition occurred after age 1, during which the timing of seaward migration of smolts was different. The marine component of the isotope variation in sockeye salmon otoliths (ages > 2) was uniform but showed a consistent and strong shift towards oceanic changes around 1996. Thus, δ18O and δ13C values of otoliths can be potentially used as a chemical tracer in population identification, and their marine portions can be used in the study of ocean environmental changes.

Circulation beneath the Filchner Ice Shelf, Antarctica, and its sensitivity to changes in the oceanic environment: a case-study

We investigate the sensitivity of the ocean circulation in the Filchner Trough to changes in the large-scale oceanic environment and its impact on the mass balance of the Filchner Ice Shelf, Antarctica. Three experiments with a three-dimensional ocean model describe (i) the current situation, (ii) a scenario with increased ocean temperatures, and (iii) a scenario with reduced sea-ice formation rates on the adjacent continental shelf. in the final discussion brief results of a combined scenario with increased ocean temperatures and reduced sea-ice formation are presented. The changes from the current situation affect the circulation in the Filchner Trough, and melting and freezing processes beneath the ice shelf. The latter affect the amount and properties of Ice Shelf Water (ISW), a component of Antarctic Bottom Water. Net basal melt rates provide an overall measure for the changes: while the control run yields 0.35 m a−1 net melting averaged over the Filchner Ice Shelf area, the warming scenario results in a more than twofold increase in ice-shelf mass loss. Reduced production of High Salinity ShelfWater due to smaller sea-ice formation rates in the second scenario leads, on the other hand, to a decrease in basal mass loss, because the deep cavity is less well ventilated than in the control run. ISW is cooled and the ice shelf is stabilized under this scenario, which is arguably the more likely development in the southern Weddell Sea.

The Vendian-Cambrian δ 13C record, North Iran: evidence for overturning of the ocean before the Cambrian Explosion

Continuous fossilliferous successions across the Precambrian/Cambrian (PC/C) boundary in the Elburz Mountains of Northern Iran show a remarkable negative δ 13C excursion just below the PC/C boundary. High concentrations of manganese, phosphorus, barium, and high abundances of fossil phytoplankton, and black shale coincide with the excursion. Worldwide stratigraphic correlation shows that the isotopic anomaly is a global event. The initial Metazoan diversification, coupled with 13C enrichment, occurs stratigraphically just above the excursion. We propose the following scenario for oceanic environmental changes before the Cambrian Faunal Explosion based on new data from Iran: A global warm climate following the last Precambrian glaciation resulted in a generally stagnant oceanic condition, so that surface water was oxic; deep water was dysoxic, depleted in 13C, and enriched in nutrients. Massive upwelling of deep water (vertical advection of nutrients and 13C-depleted CO 2) caused enhanced phytoplankton productivity and a sharp drop in δ 13C in shallow water carbonate and organic carbon. We conclude that latest Cryptozoic overturning of ocean stratification preceded the Cambrian Explosion.

Late glacial sea level and ocean margin environmental changes interpreted from biostratigraphic and lithostratigraphic studies of isolation basins in northwest Scotland

Abstract Detailed biostratigraphic and lithostratigraphic analyses from isolation basins at Ardtoe, Rumach, Loch nan Eala and Fearnbeg, northwest Scotland, allow an interpretation of sea level movements and environmental changes within the Lateglacial Interstadial and Younger Dryas (13-10 ka BP ). Microfossil analyses illustrate the gradual transition of the isolation basins from marine basins to freshwater lakes within an area of isostatic uplift. These data provide evidence for a fall in relative sea level in northwest Scotland from the mid-Lateglacial Interstadial to the early Holocene. Pollen, diatom and dinoflagellate cyst (dinocyst) analyses link the oceanic record of major climate and oceanic circulation changes with the terrestrial biostratigraphic record. Movement of the oceanic Polar Front west and north during a period of relative climatic amelioration within the Lateglacial Interstadial and a corresponding change in the position of the North Atlantic Current may be inferred from the dinocyst record. This is followed by a relative cooling.

Ecological stasis and saltation: species richness change in planktic foraminifera during the late Paleocene to early Eocene, DSDP Site 577

Abstract A high resolution study of late Paleocene to early Eocene planktic foraminifera at DSDP Site 577 indicates the presence of three rapid faunal turnovers, or saltation events, with durations varying between 200–400 kyr and species turnover rates between 4–12 species/100 kyr. These saltation events are separated by slow faunal turnovers, or stasis intervals, with durations varying between 2.56–5.21 Myr and species turnover rates between 0.6–1.8 species/100 kyr. Each saltation event has different characteristics with disappearances equal to appearances in event T1, appearances dominate in event T2 that nearly double species richness, and primarily disappearances in event T3 that nearly halve species richness. Only event T2 near the P E boundary is associated with major and sudden environmental changes, as marked by a rapid warming in the deep ocean and high-latitude surface ocean and a negative excursion in carbonate δ13C values, that suggest a cause-effect relationship. The other two events occur during intervals of gradual environmental changes. We suggest that all three faunal events are triggered by the attainment of threshold conditions during the oceanic environmental changes. Threshold conditions may be attained through rapid environmental changes as in the case of event T2 near the P E boundary, or by gradual though cumulative environmental changes as appears to be the case in events T1 and T3. It is unclear, however, which environmental factors (e.g., temperature, salinity, nutrients, water-mass stratification) force rapid faunal turnovers or what role intrinsic biotic factors play.

Southern Ocean environmental changes: effects on seabird, seal and whale populations

The main changes in the distribution and abundance of marine top predators in the Antarctic in the last two centuries were caused by hum an over-exploitation. Hypotheses that increases in populations of krill-eating penguins and seals represent recovery from exploitation, accelerated by removal of krill-eating whales, are being re-evaluated in the light of correlations between population size and reproductive success of seabirds and seals and various features of the biological and physical environment. These correlations involve phocid and otariid seals, penguins and flying birds and sites ranging from the Antarctic continent to sub-Antarctic islands. Although the nature of, and balance between, physical and biological influences differ between sites, regions and different types of predator, processes (including potentially important links with the Southern Oscillation) involving sea-ice extent and distribution play a key role. Major uncertainties over the nature of the links between physical and biological processes and the responses of marine populations preclude any confident prediction of the potential effects of future environmental change. However, certain taxa, especially those of specialist ecology, extreme demography and restricted distribution (especially in high latitudes) are especially vulnerable to at least some of the likely environmental changes.

Oceanic environmental change from the last glacial to postglacial periods

Oceanic environmental change from the last glacial to postglacial periods