Tropical Ocean Climate Research Articles

Analysis of Characteristics and Turbulent Mixing of Seawater Mass in Lombok Strait

The Lombok Strait, as one of the outlet straits, is part of the ITF route, which is directly adjacent to the Indian Ocean. There is a sill in the Lombok Strait, which is a place for internal wave generation. Leg-1 data from the Japan Agency for Marine-Earth Science and Technology in collaboration with the Agency for the Assessment and Application of Technology which is part of the Tropical Ocean Climate Study Expedition including CTD Yoyo and ADCP taken using ship vehicles R/V Kaiyo. CTD Snapshot from PUSHIDROSAL using the KRI Spica 934 vehicle part of the Opssurta Baruna Jaya 2 Expedition. Determination of seawater mass stratification with the criteria for the thermocline layer is ≥ 0.05 °C.m-1. Four types of water masses were identified, Java Sea, mixed seawater mass (Java Sea - ITF) which occurred diapycnal mixing, North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW). The seawater mass stratification in the Lombok Strait based on temperature, salinity and density which are seen to follow the internal tidal pattern. The average values for energy dissipation and vertical diffusivity for each layer and replication were 5.73 x 10-7 W.Kg-1 and 3.67 x 10-2 m2.s-1 for CTD Yoyo and 2.25 x 10-6 W.Kg-1 and 7.38 x 10-2 m2.s-1 for CTD Snapshot. The value obtained is greater than the open ocean and straits in other studies. The high shear value confirms this in the thermocline layer. The Richardson gradient value> 0.25 is relatively constant in the thermocline layer.

Gain of one-month lead time in seasonal prediction of Indian summer monsoon prediction: comparison of initialization strategies

Reasonable seasonal prediction skill for the Indian summer monsoon rainfall has been achieved using the Monsoon Mission (MM) Seasonal Forecast model, at a lead time of 3 months. The ensembles in the MM model are generated by utilizing lagged initial conditions. The possibility of enhancing the lead time is explored by using the burst ensemble approach. Comprehensive seasonal hindcast experiments carried out in this study reveal that the two methods exhibit similar skill scores for the major tropical phenomenon which govern ISMR variability. In general, the model forecasts are slightly under-dispersive but satisfactorily represent the spread-error relationship for major tropical oceanic climate modes. The ratio between the spread and RMSE is small for ISMR forecasts. Though the skill scores for the majority of indices are similar, the monsoon teleconnections seem to be quite sensitive to the initialization strategy. It is found that the burst initialization method provides a gain of 1-month lead time compared to lagged initialization strategy employed in previous studies without compromising the prediction skill. The gain of a months’ lead time with the burst ensemble approach is a tempting and useful proposition, which can be crucial for the policy- and decision-makers.

Anthropogenic effects on tropical oceanic climate change and variability: An insight from the South China Sea over the past 2000 years

To better understand the effect of human activities on tropical oceanic climate change, existing coral-based paleoclimate data from the northern South China Sea (SCS) for several representative climate periods over the past 2000 years were synthesized and reanalyzed. The sea surface temperature (SST) during the current warm period (CWP), in which the climate has been influenced by human activities, exhibits larger change amplitude and higher oscillation frequency than during periods in which the climate was controlled by natural forcings. However, the variabilities of the sea water δ18O (δ18Osw) during the four climate periods over the past 2000 years examined here are somewhat complicated to decipher. The variation amplitudes are variable but the interannual oscillations are similar during different periods. Even so, high variability during the CWP may still suggest the anthropogenic effects on tropical oceanic hydroclimate. This may implies that the anthropogenic effects intensify the tropical SST and hydrological variation both in amplitude and frequency. The decoupling between coral δ13C and total solar insolation during the CWP may be a result of the oceanic δ13C Suess effect from the addition of anthropogenic 12CO2 to the surface ocean. This suggests that increased anthropogenic CO2 caused the main carbon source and the utilization process of coral reefs during calcification to change. To accurately assess the influence of human activities on oceanic climate and environmental change, the effects of anthropogenic CO2 should be monitored continuously over a longer time frame.

Clay Compaction Test for the Core Wall of DJIPLOHO Dam

The earth-rock dam on left bank of the head of DJIPLOHO Hydroelectric Power Station adopts the clay core dam. Due to the tropical oceanic climate which is hot and rainy, the soil of clay core wall has high water content. Through the compaction experiment on site, it chooses suitable dry density, formulates reasonable rolling parameters and finally achieves good construction quality, which ensures the construction progress and meets the requirement of engineering. This accumulates valuable experience for the design and construction of same types engineering.

Coupled imprints of tropical climate and recurring emergence on reservoir evolution of a mid Cretaceous carbonate ramp, Zagros Basin, southwest Iran

The Cretaceous Sarvak Formation (and its equivalents on the Arabian platform) is one of the most important carbonate reservoirs to have developed under the warm equable climate. This formation in the Abteymour Oilfield contains a hydrocarbon reservoir in a carbonate ramp formed under a humid tropical oceanic climate during the middle Cretaceous in the far southwest margin of Zagros Basin, in the transition zone of the Mesopotamian Basin and Dezful Embayment. Detailed petrography assisted by image analysis resulted in the recognition of 12 microfacies grouped in six facies associations indicating a homoclinal ramp-type platform. The importance of climatic control over the facies types and patterns and diagenetic history is elaborated in this study. Interactions of sea-level fluctuations, local tectonic activity and climate are reflected by the substantial dissolution and development of reservoir quality in different horizons of this mud-dominated carbonate unit. The history of reservoir formation and its evolution during post-depositional events are revealed by a high-resolution study of primary and secondary textural features and their relationships. Accordingly, the relative timing of these processes and their paragenetic sequences indicate a complex reservoir history. From the Late Albian to the Mid Turonian three phases of emergence originated from eustatic changes and movements of basement blocks (palaeohigh formation), which led to extensive leaching and karstification. The Mid Cenomanian eustatic sea-level fall led to the first disconformity. A second emergent period and disconformity was the result of Late Cenomanian–Early Turonian movement of basement blocks. An Early–Middle Turonian sea-level rise or local subsidence of the palaeohigh led to inundation of this area and deposition of the upper division of the Sarvak Formation. This buried the middle Sarvak Formation to shallow depths and caused some cementation and mechanical compaction. A widespread Mid Turonian fall in sea level and basin-wide exposure lasting several million years led to the formation of an important regional disconformity in the upper Sarvak unit, represented by major diagenetic dissolution and an over-mature karst profile. Concurrently, deep circulation of meteoric waters led to another phase of non-fabric selective leaching beneath the C–T disconformity (telogenetic diagenesis) in the middle Sarvak Formation. These two stages of diagenesis (eo- and telogenetic) resulted in considerable improvement of the reservoir in the middle Sarvak succession. Generally, these diagenetic features show a good correlation with depositional facies and sequence stratigraphic positions (systems tracts). As shown in this study, they are predictable in the sequence stratigraphic framework of the formation. Three third-order sequences in the Mid Cenomanian–Mid Turonian interval are recognized. These are clearly correlated over the Abteymour Oilfield and other areas in the Zagros Basin and Arabian Platform (Oman) and provide a suitable framework for reservoir correlations and further modelling.

Pacific climate variability and the possible impact on global surface CO2 flux.

BackgroundClimate variability modifies both oceanic and terrestrial surface CO2 flux. Using observed/assimilated data sets, earlier studies have shown that tropical oceanic climate variability has strong impacts on the land surface temperature and soil moisture, and that there is a negative correlation between the oceanic and terrestrial CO2 fluxes. However, these data sets only cover less than the most recent 20 years and are insufficient for identifying decadal and longer periodic variabilities. To investigate possible impacts of interannual to interdecadal climate variability on CO2 flux exchange, the last 125 years of an earth system model (ESM) control run are examined.ResultsGlobal integration of the terrestrial CO2 flux anomaly shows variation much greater in amplitude and longer in periodic timescale than the oceanic flux. The terrestrial CO2 flux anomaly correlates negatively with the oceanic flux in some periods, but positively in others, as the periodic timescale is different between the two variables. To determine the spatial pattern of the variability, a series of composite analyses are performed. The results show that the oceanic CO2 flux variability peaks when the eastern tropical Pacific has a large sea surface temperature anomaly (SSTA). By contrast, the terrestrial CO2 flux variability peaks when the SSTA appears in the central tropical Pacific. The former pattern of variability resembles the ENSO-mode and the latter the ENSO-modoki1.ConclusionsOur results imply that the oceanic and terrestrial CO2 flux anomalies may correlate either positively or negatively depending on the relative phase of these two modes in the tropical Pacific.

Flow injection analysis of nitrate-N determination in root vegetables: Study of the effects of cooking

Abstract Vegetables are the major vehicles for the entry of nitrate into the human system. Ever-increasing concern over nitrate toxicity has directed a number of countries to lay down maximum allowable threshold concentrations with regards to nitrate-N in vegetables. Fiji is an independent island nation, located in the southern Pacific Ocean, has a tropical oceanic climate and hence expected to have high nitrate-N levels in vegetables. Thus, the present study was devoted to establish a flow injection analysis (FIA) technique for nitrate-N determination in Fiji’s commonly consumed fresh and cooked root vegetables such as potato (Solanum tuberosum), dalo (Colocasia esculenta), sweet potato (Ipomoea batatas) and carrot (Daucus carota L.). Activated carbon extraction technique was applied to extract nitrate-N. FIA with colorimetric detection technique having linear dynamic range of determination 1.0–20.0 mg L−1 and detection limit of 0.042 mg L−1 (0.34 mg kg−1), using sulphanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride as colour reagents, was used to determine nitrate-N contents in selected fresh and cooked root vegetables. The samples throughput was 38 h−1. The effects of various cooking (boiling, baking and frying) methods on nitrate-N contents in root vegetables have also been studied. The study shows that the nitrate content of fresh root vegetables ranges from 53.76–258.00 mg kg−1 whereas boiling reduces nitrate content by 23.30–42.62%. The frying in soya bean oil elevates nitrate contents from 204.53–299.12% but after baking nitrate contents remains almost constant with slight increasing trend from 2.80–8.43%. A comparison of the nitrate obtained by standardised method and the nitrate contents in vegetables of other countries are also presented.

Climate Fluctuations of Tropical Coupled Systems—The Role of Ocean Dynamics

Abstract The tropical oceans have long been recognized as the most important region for large-scale ocean–atmosphere interactions, giving rise to coupled climate variations on several time scales. During the Tropical Ocean Global Atmosphere (TOGA) decade, the focus of much tropical ocean research was on understanding El Niño–related processes and on development of tropical ocean models capable of simulating and predicting El Niño. These studies led to an appreciation of the vital role the ocean plays in providing the memory for predicting El Niño and thus making seasonal climate prediction feasible. With the end of TOGA and the beginning of Climate Variability and Prediction (CLIVAR), the scope of climate variability and predictability studies has expanded from the tropical Pacific and ENSO-centric basis to the global domain. In this paper the progress that has been made in tropical ocean climate studies during the early years of CLIVAR is discussed. The discussion is divided geographically into three tropical ocean basins with an emphasis on the dynamical processes that are most relevant to the coupling between the atmosphere and oceans. For the tropical Pacific, the continuing effort to improve understanding of large- and small-scale dynamics for the purpose of extending the skill of ENSO prediction is assessed. This paper then goes beyond the time and space scales of El Niño and discusses recent research activities on the fundamental issue of the processes maintaining the tropical thermocline. This includes the study of subtropical cells (STCs) and ventilated thermocline processes, which are potentially important to the understanding of the low-frequency modulation of El Niño. For the tropical Atlantic, the dominant oceanic processes that interact with regional atmospheric feedbacks are examined as well as the remote influence from both the Pacific El Niño and extratropical climate fluctuations giving rise to multiple patterns of variability distinguished by season and location. The potential impact of Atlantic thermohaline circulation on tropical Atlantic variability (TAV) is also discussed. For the tropical Indian Ocean, local and remote mechanisms governing low-frequency sea surface temperature variations are examined. After reviewing the recent rapid progress in the understanding of coupled dynamics in the region, this study focuses on the active role of ocean dynamics in a seasonally locked east–west internal mode of variability, known as the Indian Ocean dipole (IOD). Influences of the IOD on climatic conditions in Asia, Australia, East Africa, and Europe are discussed. While the attempt throughout is to give a comprehensive overview of what is known about the role of the tropical oceans in climate, the fact of the matter is that much remains to be understood and explained. The complex nature of the tropical coupled phenomena and the interaction among them argue strongly for coordinated and sustained observations, as well as additional careful modeling investigations in order to further advance the current understanding of the role of tropical oceans in climate.

Sharp frontal interfaces in the near-surface layer of the tropical ocean

The small-scale structure of oceanic fronts contains important information about horizontal and vertical exchange of properties in the upper ocean. The data obtained in the western equatorial Pacific warm pool during Tropical Ocean–Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) and Tropical Ocean Climate Study (TOCS) suggest that the sharp frontal interfaces occasionally observed in the upper layer of the tropical ocean may be associated with gravity currents. These gravity currents originate from the surface pools of relatively low-density (fresh and/or warm) water produced by convective rainfalls and spatially variable diurnal warming. It has been shown that frontal interfaces of less than 100 m width may interact with wind stress via the mechanism of Stommel's “overturning gate.” The anisotropy of sharp frontal interfaces with respect to the wind stress direction can be predicted with a simple nonlinear model including both dissipation and dispersion effects. This study elucidates the role of fronts in the dynamics of the tropical ocean and provides important details to the description of how the temperature–salinity relationship and barrier layer in the warm pool areas are formed.

Vast Neogene laminated diatom mat deposits from the eastern equatorial Pacific Ocean

THE eastern equatorial Pacific upwelling region is responsible for up to 50% of global 'new' production1 and is regarded as a barometer of ocean change. Here we report evidence, from several sediment cores in the region, for repeated episodes of increased equatorial primary production between 15 and 4.4 million years ago, on a scale that is undocumented in the modern ocean. Mats of the diatom Thalassiothrix were rapidly deposited as successive laminations at rates exceeding 10cm per thousand years; mat deposits can be correlated for distances of more than 2,000 km. It is surprising that the laminations were preserved at all: conventional models suggest that bioturbation caused by the benthic sediment community will disrupt such laminations unless there is insufficient oxygen in the water to support the biological activity. In this case, however, the strength of the mats and the scale of their deposition may have overwhelmed the benthos, so that the laminations were preserved by physical means. These remarkable deposits provide a unique window into the Neogene tropical ocean–climate system, and should enable quantification of ancient deep-sea fluxes and the study of short-term (sub-Milankovitch) variability in the ocean.

Exsiccatae of the Bryophytes of Taiwan

Exsiccatae of the Bryophytes of Taiwan, issued in 1981, were dis- tributed in two-hundred and fifty numbers in five series. Because of Taiwan's geographical position, its complicated topography as well as its subtropical and tropical oceanic climate, the microhabitats suitable for the growth of var- ious bryophytes are numerous. The bryophytic flora of Taiwan includes 1029 species (Lai & Wang-Yang 1976). When compared with other islands to the south-east and in Oceania, the number of species of mosses in Taiwan (644 spp.) is next to that of New Guinea (933 spp.), which is regarded by Schultze-Motel (1975) as a main center of moss evolution. However, the density of Taiwan mosses (644 spp./3600 sq km) is 1.5 times as many as that of New Guinea (930 spp./900,000 sq km). It is also of interest to mention that the density of the genera of phanerogams in the two areas reflects the same ratio (Paijmans 1976). In the history of bryological exploration of Taiwan, the earlier extensive collections were made mainly by A. Noguchi (1928, 1932; herb. Noguchi, HIRO, NICH & herb. Makino) and Y. Horikawa (1932, 1933, 1934, 1935; HIRO). Since then, important collections from Taiwan have been provided by T. Shin (1939; herb. Shin & herb. Makino), C. K. Wang (1958-; herb. Tunghai University, Taichung, Taiwan-THU & NICH), H. Ando (HIRO), S. Nakanishi (1963; herb. Kobe Univ., Kobe, Japan & NICH), Z. Iwatsuki & A. J. Sharp (1965; NICH & TENN), S. Lin (1967-; THU), C. Chuang (1967-1968; TAI & UBC), M. J. Lai (1970-; TAI), T. Koponen (1970; TAI & H), H. Ochi (1978; herb. Ochi), K. Yamada, Y. Yuzawa & Ogasawara (1979; herb. Yamada, NICH, TAI). Most of the type specimens of bryophytes from the island are deposited in G, B, JE, H, HIRO, herb. Makino, NICH, herb. Noguchi, THU, and TAI. In view of the bryophytes of Taiwan being poorly represented in many of the herbaria in the world, the author issued five series of Exsiccatae of the Bryophytes of Taiwan in 1981. Each series contains 50 members. At present, the herbaria in which sets of the exsiccatae have been deposited are: ALTA, MICH, H, HAREN, MO (incomplete set), NICH, NY, PAC, TAI (incomplete set), THU, and UBC. Following is a list of the taxa represented in the five series.