Equatorial Indian Research Articles

Role of a Cyclonic Eddy in the 7000-Year-Old Mentawai Coral Reef Death During the 1997 Indian Ocean Dipole Event

A major discovery on the coral fronts was the death of the 7000-year-old coral reefs along the Mentawai Islands located offshore of southwest Sumatra, Indonesia, in the equatorial eastern Indian Ocean due to the Indian Ocean Dipole event of 1997. Using two ocean general circulation models, the NASA Ocean Biogeochemistry Model and Estimating the Circulation and Climate of the Ocean Model, we investigate the variability in nitrate influx, mixed layer depth (MLD), and surface currents over the region 0°-8° S; 90°-106° E. An enhanced nitrate influx by 6.5 micromoles (3150% higher than the mean), a lower MLD by 5 m (300% lower than the mean), and a massive cyclonic eddy (400 km meridonally and 500 km zonally) are observed over the region 4°-8° S; 94°-100° E (along the region of coral mortality) for three months (November and December 1997 and January 1998). Cyclonic eddies enhance phytoplankton and primary productivity, but when in the proximity of a coral reef, they can destroy the coral colony through asphyxiation caused by massive phytoplankton blooms. The results bring to the fore the importance of mesoscale processes that significantly impact the health of coral reefs.

Propagating Coupled Modes between the Tropical Indo-Pacific Ocean Heat Content and SST Anomalies in the Interannual Timescale

This study uses a time-mode extended singular value decomposition (TESVD) analysis to identify the propagating coupled modes between the upper ocean heat content (UOHC) and sea surface temperature (SST) anomalies in the tropical Indo-Pacific. Four dominant TESVD modes stand out in the interannual timescale. The TESVD1 and TESVD2 depict the thermocline-SST feedback process during ENSO’ persistence period and its turnabout, respectively. With an intrinsic 42-month periodicity, both modes together form an UOHCA pattern propagating counterclockwise around the circuit of equatorial-to-northern tropical Pacific followed by the SSTA propagating eastward in the equatorial waveguide. The leading role of UOHCA is mainly associated with El Nino occurrence. In contrast, the TESVD3 depicts the onset stage of ENSO that has the westward propagating SSTA lead the UOHCA in the cold tongue region. Suppressed equatorial upwelling directly through the positive feedback between the warmer SSTs and anomalous wind convergence from the northwestern Pacific and Caribbean Sea is another factor to trigger El Nino over the NINO3 region, in addition to the thermocline-SST feedback. The TESVD4 depicts the low-frequency evolution of SSTA when ENSO signal is absent. It has the westward migrating SSTA lead the UOHCA 4-month in the equatorial East Pacific. However, the pace of coupled UOHCA is nearly stagnant elsewhere due to the lack of thermocline adjustment mechanism when the zonal wind anomalies largely disappear over the equatorial Indian and West Pacific Oceans. In the Indian Ocean, while the ENSO-related SSTA evolution mainly displays an eastward basin-scale change in the first two TESVD modes, SSTA pattern depicted by the TESVD3 (TESVD4) resembles the double (single) polarity of the Indian Ocean dipole (IOD) event. It is mainly in its east pole region of southeastern Indian Ocean that the SSTA evolution tends to decouple with the underlying UOHCA.

Sensitivity of Tropical Rainfall to Banda Sea Diffusivity in the Community Climate System Model

Abstract Several observational studies suggest that the vertical diffusivity in the Indonesian marginal seas is an order of magnitude larger than in the open ocean and what is used in most ocean general circulation models. The experiments described in this paper show that increasing the background diffusivity in the Banda Sea from the commonly used value of 0.1 cm2 s−1 to the observed value of 1 cm2 s−1 improves the watermass properties there by reproducing the observed thick layer of Banda Sea Water. The resulting reduced sea surface temperatures lead to weaker convection and a redistribution of precipitation, away from the Indonesian seas toward the equatorial Indian and Pacific Oceans. In particular, the boreal summer precipitation maximum of the Indonesian seas shifts northward from the Banda Sea toward Borneo, which reduces a longstanding bias in the simulation of the Austral–Asian Monsoon in the Community Climate System Model. Because of the positive feedback mechanisms inherent in tropical atmosphere dynamics, a reduction in Banda Sea heat loss of only 5% leads locally to a reduction in convection of 20%.

Does the Madden‐Julian Oscillation influence aerosol variability?

We investigate the modulation of aerosols by the Madden‐Julian Oscillation (MJO) using multiple, global satellite aerosol products: aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus‐7, and aerosol optical thickness (AOT) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua and the Advanced Very High Resolution Radiometer (AVHRR) on NOAA satellites. A composite MJO analysis indicates that large variations in the TOMS AI and MODIS/AVHRR AOT are found over the equatorial Indian and western Pacific Oceans where MJO convection is active, as well as the tropical Africa and Atlantic Ocean where MJO convection is weak but the background aerosol level is high. A strong inverse linear relationship between the TOMS AI and rainfall anomalies, but a weaker, less coherent positive correlation between the MODIS/AVHRR AOT and rainfall anomalies, were found. The MODIS/AVHRR pattern is consistent with ground‐based Aerosol Robotic Network data. These results indicate that the MJO and its associated cloudiness, rainfall, and circulation variability systematically influence the variability in remote sensing aerosol retrieval results. Several physical and retrieval algorithmic factors that may contribute to the observed aerosol‐rainfall relationships are discussed. Preliminary analysis indicates that cloud contamination in the aerosol retrievals is likely to be a major contributor to the observed relationships, although we cannot exclude possible contributions from other physical mechanisms. Future research is needed to fully understand these complex aerosol‐rainfall relationships.

A glacial warm water anomaly in the subantarctic Atlantic Ocean, near the Agulhas Retroflection

ODP Site 1089 is optimally located in order to monitor the occurrence of maxima in Agulhas heat and salt spillage from the Indian to the Atlantic Ocean. Radiolarian-based paleotemperature transfer functions allowed to reconstruct the climatic history for the last 450 kyr at this location. A warm sea surface temperature anomaly during Marine Isotope Stage (MIS) 10 was recognized and traced to other oceanic records along the surface branch of the global thermohaline (THC) circulation system, and is particularly marked at locations where a strong interaction between oceanic and atmospheric overturning cells and fronts occurs. This anomaly is absent in the Vostok ice core deuterium, and in oceanic records from the Antarctic Zone. However, it is present in the deuterium excess record from the Vostok ice core, interpreted as reflecting the temperature at the moisture source site for the snow precipitated at Vostok Station. As atmospheric models predict a subtropical Indian source for such moisture, this provides the necessary teleconnection between East Antarctica and ODP Site 1089, as the subtropical Indian is also the source area of the Agulhas Current, the main climate agent at our study location. The presence of the MIS 10 anomaly in the δ 13C foraminiferal records from the same core supports its connection to oceanic mechanisms, linking stronger Agulhas spillover intensity to increased productivity in the study area. We suggest, in analogy to modern oceanographic observations, this to be a consequence of a shallow nutricline, induced by eddy mixing and baroclinic tide generation, which are in turn connected to the flow geometry, and intensity, of the Agulhas Current as it flows past the Agulhas Bank. We interpret the intensified inflow of Agulhas Current to the South Atlantic as responding to the switch between lower and higher amplitude in the insolation forcing in the Agulhas Current source area. This would result in higher SSTs in the Cape Basin during the glacial MIS 10, due to the release into the South Atlantic of the heat previously accumulating in the subtropical and equatorial Indian and Pacific Ocean. If our explanation for the MIS 10 anomaly in terms of an insolation variability switch is correct, we might expect that a future Agulhas SSST anomaly event will further delay the onset of next glacial age. In fact, the insolation forcing conditions for the Holocene (the current interglacial) are very similar to those present during MIS 11 (the interglacial preceding MIS 10), as both periods are characterized by a low insolation variability for the Agulhas Current source area. Natural climatic variability will force the Earth system in the same direction as the anthropogenic global warming trend, and will thus lead to even warmer than expected global temperatures in the near future.

Atmosphere–Warm Ocean Interaction and Its Impacts on Asian–Australian Monsoon Variation*

Asian–Australian monsoon (A–AM) anomalies depend strongly on phases of El Niño (La Niña). Based on this distinctive feature, a method of extended singular value decomposition analysis was developed to analyze the changing characteristics of A–AM anomalies during El Niño (La Niña) from its development to decay. Two off-equatorial surface anticyclones dominate the A–AM anomalies during an El Niño—one over the south Indian Ocean (SIO) and the other over the western North Pacific (WNP). The SIO anticyclone, which affects climate conditions over the Indian Ocean, eastern Africa, and India, originates during the summer of a growing El Niño, rapidly reaches its peak intensity in fall, and decays when El Niño matures. The WNP anticyclone, on the other hand, forms in fall, attains maximum intensity after El Niño matures, and persists through the subsequent spring and summer, providing a prolonged impact on the WNP and east Asian climate. The monsoon anomalies associated with a La Niña resemble those during an El Niño but with cyclonic anomalies. From the development summer to the decay summer of an El Niño (La Niña), the anomalous sea level pressure, low-level winds, and vertical motion tend to reverse their signs in the equatorial Indian and western Pacific Oceans (10°S–20°N, 40°–160°E). This suggests that the tropospheric biennial oscillation is intimately linked to the turnabouts of El Niño and La Niña. The remote El Niño forcing alone can explain neither the unusual amplification of the SIO anticyclone during a developing El Niño nor the maintenance of the WNP anticyclone during a decaying El Niño. The atmosphere–ocean conditions in the two anticyclone regions are similar, namely, a zonal sea surface temperature (SST) dipole with cold water to the east and warm water to the west of the anticyclone center. These conditions result from positive feedback between the anomalous anticyclone and the SST dipole, which intensifies the coupled mode in the SIO during El Niño growth and maintains the coupled mode in the WNP during El Niño decay. The interactions in the two anticyclone regions share common wind evaporation/entrainment and cloud–radiation feedback processes but they differ with regard to the oceanic dynamics (vertical and horizontal advection and thermocline adjustment by oceanic waves). The outcome of the interactions in both regions, however, depends crucially on the climatological surface winds. The SIO-coupled mode is triggered by El Niño-induced subsidence and alongshore winds off the coast of Sumatra. However, other independent El Niño local and remote forcing can also trigger this coupled mode. The traditional view has regarded SST anomalies in the Indian and western Pacific Oceans as causing the A–AM variability. The present analysis suggests that the SST anomalies in these warm ocean regions are, to a large extent, a result of anomalous monsoons. Thus, the atmosphere–warm ocean interaction may significantly modify the impacts of remote El Niño forcing and should be regarded as one of the physical factors that determine the variability of the A–AM. During the summer of El Niño development, the remote El Niño forcing plays a major role in the A–AM anomalies that exhibit obvious equatorial asymmetry. A tilted anticyclonic ridge originates in the Maritime Continent and extends to southern India, weakening the Indian monsoon while strengthening the WNP monsoon. Numerical modeling experiments suggest that the mean monsoon circulation enhances the equatorial Rossby wave response in the easterly vertical shear region of the Northern Hemisphere and creates the equatorial asymmetry.

Interdecadal changes in the zonal wind and the intensity of intraseasonal oscillations during boreal summer Asian monsoon

Decadal’interdecadal changes in the intensity of intraseasonal oscillations (ISO) and in thesummer mean wind fields in the Asian monsoon system are investigated using 51 yr of 850 hPazonal wind data obtained from the National Centers for Environmental Prediction — NationalCenter for Atmospheric Research (NCEP/NCAR) Reanalysis. Decadal’interdecadal variationscontribute significantly to the total variability of the summer mean 850 hPa zonal wind(30—45%) and the ISOs intensity (20—35%). These variations in the summer mean 850 hPazonal wind and in the intensity of the 30—60 d ISO have a distinct zonal structure and areassociated with the strength of low level westerlies and with meridional dynamics of the TropicalConvergence Zone (TCZ). Interdecadal changes in the intensity of the 10—20 d ISO are mostpronounced over the eastern Indian Ocean, the South China Sea and the western tropical Pacific.Singular value decomposition (SVD) analysis revealed a strong correlation on an interdecadaltimescale between the sea surface temperatures (SST) in the Indian Ocean and the summermean 850 hPa zonal wind and the intensity of the ISOs in the Asian summer monsoon, whereassuch correlations on a decadal timescale are weak. The temporal expansion coefficients of thefirst SVD mode show a climate regime shift in the mid-late 1970s. During the last few decades, SST in the Indian Ocean increased, resulting in a decreased land’sea heat contrast and weakerlow-level westerlies over northern Indian Ocean, the Indian subcontinent, and Indochina. Inresponse to sea surface warming and associated enhanced convection, the 30—60 d ISO becamestronger over the equatorial central and western Indian Ocean and the South China Sea, andweaker over the Indian subcontinent, the northern Arabian Sea and the Bay of Bengal.Meanwhile a 10—20 d ISO intensified over the eastern Indian Ocean, the South China Sea, andthe western tropical Pacific.

Globorotalia truncatulinoides as indicator of upper-ocean thermal structure during the Quaternary: evidence from the South China Sea and Okinawa Trough

Globorotalia truncatulinoides is shown to be indicative of upper-ocean thermal structure and sensitive to the thermocline fluctuations and the thickness of the North Pacific subtropical mode water (NPSTMW) thermostads for the Quaternary in the South China Sea (SCS) and Okinawa Trough. During the last 1.5 Ma, the relative abundance (percentage) of G. truncatulinoides displayed long-term oscillations on a time scale longer than the glacial–interglacial cycle, but with two major changes around 550–400 ka and 115–55 ka BP. It decreased to near zero during 550–400 ka BP and then disappeared from the equatorial Indian and Pacific Oceans. This suggests that the thermocline depth and the scale of winter deep-mixing decreased at that time interval, and since then the linkage between the SCS and the equatorial oceans at intermediate depths remarkably weakened and the NPSTMW strongly influenced the SCS. The predominance of left-coiling G. truncatulinoides together with the occurrence of Globoquadrina conglomerata in the western North Pacific between 115 and 55 ka BP indicates a deep thermocline and very thick NPSTMW thermostads. A decreasing trend in the relative abundance of G. truncatulinoides from marine isotopic stages 7 to 1 is evident in the SCS, indicating a progressive reduction of the NPSTMW thermostads. After the last glacial maximum, G. truncatulinoides increased in abundance, but abruptly disappeared between 8 and 4 ka BP from the SCS and Okinawa Trough, implying a mid-Holocene reduction in the NPSTMW thermostad thickness.

Wavenumber spectra of horizontal wind and temperature measured with WINDII, Part I: observational results

The horizontal wind and temperature data inferred from the WINDII green line observations are used to derive global maps of vertical and horizontal wavenumber spectra, and to investigate the temporal/geographic variations of atmospheric wave motions. The planetary-scale disturbances between 90 and 120 km in September 1995 were found to be characterized by large r.m.s. velocities of ∼30–45 m/s and fractional temperatures of ∼5–9%, with maximum velocity variances in the region over the equatorial Indian – Central Pacific Oceans. In contrast, the small-scale gravity waves displayed mean fluctuation amplitudes of ∼18–30 m/s and 3–6%, with the maxima at mid-latitudes. The velocity variances of both scales slowly increased with increasing altitude at the lower heights, with a faster growth for the large-scale waves, but remained virtually constant above ∼105 km due to the wave breaking and saturation. The results also revealed strong correlations between the longitudinal and temporal variations of the large- and small-scale waves. Vertical and horizontal wavenumber spectra observed at different locations and times showed great similarities, respectively, confirming the notion of “universality”. However, significant temporal/geographic variations were found to exist, in respose to the changes in the wave source mechanisms and/or the interaction of gravity waves with, and their filtering by, the variable environment.

Operational long-lead prediction of South African rainfall using canonical correlation analysis

A statistically based technique is used to study the variability and predictability of South African summer rainfall. The country is divided into homogeneous regions on the basis of the interannual rainfall variability. Canonical variates are then used to make 3-month aggregate precipitation forecasts for October–November–December and January–February–March for South Africa from global-scale sea-surface temperatures. Four consecutive 3-month mean periods of sea-surface temperatures are used to incorporate evolutionary features as well as steady-state conditions in the global oceans. Levels and possible origins of forecast skill are investigated for up to 5-month lead-times. Modest skill (correlation >0.5) is found over mainly the central and western interiors of the country, but the skill is poor over the north-eastern regions. The most important contribution of the prediction skill comes from the equatorial Pacific Ocean, with weaker predictability from the equatorial Indian and Atlantic oceans. Sea-surface temperatures in the Atlantic and Indian oceans have important influences on the atmospheric circulation and moisture fluxes over southern Africa, and therefore provide useful predictability, at least for the October–December rainfall. When forecasting South African rainfall, it is insufficient to consider only the El Nino–Southern Oscillation (ENSO) phenomenon, because it does not occur every year and because the sea-surface temperatures of the adjacent oceans modify the ENSO forcing on South African rainfall. Unfortunately, the predictability during years not associated with the ENSO is weak. Copyright © 1999 Royal Meteorological Society

Late Neogene Radiolarian Events in Andaman-Nicobar Islands, Northeast Indian Ocean

Eleven radiolarian events are identified in the Late Miocene to Early Pliocene sequences of the Andaman-Nicobar Islands. Stratigraphic ranges of important taxa are discussed and events are compared with those in sediments from the Central Indian Basin and Site 214 in the Indian Ocean and Sites 289, 586, 573 and 503 in the Pacific Ocean. INTRODUCTION Deep-water Neogene sediments of the Andaman-Nicobar Islands in the Northeast Indian Ocean contain a rich and diverse radiolarian assemblage. However, radiolarian studies have been confined to a few publications (Jacob and Shrivastava 1952; Singh and Vimal 1973; Srinivasan et al. 1983; Sharma and Sharma 1988; Gupta and Srinivasan 1992; Sharma and Singh 1993; Sharma et al. 1993; and Mahapatra and Sharma 1994). The present study is the continuation of earlier analyses of the radiolarians in the sediments from Neill and Car Nicobar Islands by Sharma and Sharma (1988, 1989) and Sharma and Singh (1993). These earlier papers documented the radiolarian taxa and identified the radiolarian zones. The main purpose of the present paper is to identify radiolarian events and to examine these in relation to those recorded in the equatorial Indian and Pacific Oceans. MATERIALS AND METHODS Three sections located at Neill and Car Nicobar Islands have been examined in this study (text-figure 1). The sections contain rich and well preserved Radiolaria and provide an almost continuous record from Late Miocene to Early Pliocene. Thirty two samples from the East Coast Section, Neill Island, and sixty samples from Passa Bridge and Sawai Bay Sections, Car Nicobar Island, are examined. The stratigraphic disposition of the samples, lithologies and zonal scheme are illustrated in textfigure 2. Two to six slides for each sample were prepared from the washed fraction coarser than 63ptm. For Neill Island, slides additional to those studied by Sharma and Sharma (1989) were examined. This resulted in minor revision in the distribution of Stichocorys delmontensis and Stichocorys peregrina compared to that reported by Sharma and Sharma (op. cit.). BIOSTRATIGRAPHY AND EVENTS Based on the core samples from the Central Indian Basin, Johnson et al. (1989) using synchronous radiolarian events <0.4 Ma difference) in the tropical Indian and Pacific Oceans proposed eleven zones for the Plio-Pleistocene interval. Based on the scheme of Johnson et al., Sharma and Singh (1993) assigned the Car Nicobar sequence to Phormostichoartus doliolum, Phormostichoartus fistula and Stichocorys peregrina (non Stichocorys peregrina Zone of Riedel and Sanfilippo 1978) Zones in ascending order of age. Using the zonal scheme of Riedel and Sanfilippo (1978), the Car Nicobar sequence is assigned to Spongaster pentas Zone (Sharma and Singh, op. cit.). The events (morphotypic bottom, 'Bm' and morphotypic top, 'Tm') identified in the Car Nicobar sequence are Spongaster tetras Bm, Didymocyrtis tetrathalamus Bm, Amphirhopalum ypsilon Bm, in the Phomostichoartus doliolum Zone, and Anthocyrtidium pliocenica Tm in the Stichocorys peregrina Zone (non Stichocorys peregrina Zone of Riedel and Sanfilippo 1978). In addition, Phormostichoartus doliolum Tm and Phormostichoartus fistula Tm, are used to demarcate the zonal boundaries. Biostratigraphy of the sequence at Neill Island can be found in Sharma and Sharma (1989), according to which the sequence is divided into Didymocyrtis penultima and Stichocorys peregrina Zones of Riedel and Sanfilippo (1978) (text-figure 2). In terms of zonation by Johnson et al. (1989), the section from sample Mf 529 upwards can be assigned to the Anthocyrtidium prolatum Zone, as Anthocyrtidium prolatum first appears in sample Mf 529 and ranges through the younger samples of the examined section. The events recognised in the sequence at Neill Island, viz., Anthocyrtidium jenghisi Bm, Anthocyrtidium prolatum Bm and Spongaster pentas Bm, occur within the Stichocorys peregrina Zone. In the text we have used the zonal nomenclature of Johnson et al. (op. cit.) for the Car Nicobar sequence, for it provides a more detailed zonal scheme for the Plio-Pleistocene. However, for the Late Miocene-Early Pliocene Neill Island sequence, the zonation of Riedel and Sanfilippo (1978) has been applied. The identified events have been compared with those reported from the tropical Indian and Pacific Oceans (Table 1). Absolute ages are those of Johnson et al. (1989) and Caulet et al. (1993), except in three cases, where data from Johnson and Nigrini (1985b), Nigrini and Caulet (1988) and Theyer et al. (1978) have been used. SELECTION OF DSDP SITES FOR COMPARISON I an effort to find taxa comparable to those in the studied sections and in DSDP sites in the Indian and Pacific Oceans, we micropaleontology, vol. 43, no. 1, pp. 41-50, text-figures 1-2, plate 1, tables 1-2, appendix 1, 1997 41 This content downloaded from 207.46.13.193 on Thu, 08 Sep 2016 05:51:04 UTC All use subject to http://about.jstor.org/terms V. Sharma and Surender Singh: Late Neogene Radiolarian events in Andaman-Nicobar Islands, northeast Indian Ocean

Seasonal variations of the Indonesian throughflow in a general ocean circulation model

Seasonal variability of the depth‐integrated transport in the Indonesian Seas is investigated in detail, together with its driving mechanism, by use of an Indo‐Pacific ocean general circulation model that allows the circulation around Australasia. Modeled net throughflow shows an annual mean transport of 9.5 Sv from the Pacific to the Indian Ocean with a maximum (minimum) transport of 11.6 Sv (6.0 Sv) in August (January). Seventy‐five percent of this transport flows through the Lombok Strait in the present model. Comparison with the result of Masumoto and Yamagata [1993], in which the circulation around Australasia was not permitted, clarifies that the magnitude of the net interbasin throughflow does not affect the seasonal variations in the depth‐integrated transport through the Lombok Strait. Several additional experiments are also carried out by masking winds over particular regions to identify which part of winds is actually effective in the seasonal variations in the depth‐integrated transport through the Timor Sea as well as the Lombok Strait. It turns out that the seasonal variability of the transport through the Lombok Strait is almost perfectly governed by the winds over the equatorial Indian and Pacific Oceans. On the other hand, the coastally trapped waves generated by the winds along the western and southern coast of Australia play an important role in the seasonal transport variation through the Timor Sea.

Alveus, gen. nov. (Bacillariaceae, Bacillariophyta), a heavily silicified diatom found in warm water oceans.

Scanning electron microscope images of complete and damaged frustules of Nitzschia marina Grun. revealed an unusual chambered structure of the valve. This structure is not present in any existing nitzschioid genus and warrants an independent generic status for this taxon, which is therefore separated into Alveus gen. nov. Generic and emended specific definitions are provided and presented in the context of their relationship to other genera within the family Bacillariaceae. Deep relief of the inner surface of Alveus valves is similar to that of genera Fragilariopsis, Denticulopsis, Neodenticula, and Crucidenticula. It differs from all these diatoms in the alveolar striation. This heavily silicified diatom was found in samples from the US Joint Global Oceanographic Flux Studies cruise TT007 stations 2 and 4, (9 degrees and 5 degrees N respectively, 140 degrees W) in the equatorial Pacific. Presently, this uncommon species is restricted to warm waters. It is very common in the surface sediments of the equatorial Pacific and Indian Ocean and in the tropical and subtropical Atlantic. The sedimentary record of Alveus marinus goes back to the Middle Late Miocene (approximately 8 Ma years).

Global surface air temperature variations during the twentieth century: Part 2 , implications for large-scale high-frequency palaeoclimatic studies

This paper is the second of a two-part series analysing details of regional, hemispheric and global temperature change during the twentieth century. Based on the grid box data described in Part 1 we present global maps of the strength of regional temperature coherence measured in terms of the correlation decay length for both annual and seasonal mean data. Correlation decay lengths are generally higher for annual rather than seasonal data; higher in the Southern compared to the Northern Hemisphere; and consistently higher over the oceans, particularly the Indian and central north Pacific oceans. Spatial coherence is relatively low in all seasons over the mid to high latitudes of the Northern Hemisphere and especially low in summer over the northern North Atlantic region. We also describe selected regional temperature series and examine the similarities between these and hemispheric mean data, placing emphasis on the nature of the relationships in different seasons. The Equatorial Indian and Atlantic oceans appear to be the best regional proxies for representing global mean temperatures. Temperature change in regions bordering the northern North Atlantic are less representative of hemisphere mean data, particularly in summer. The implications of these results for the large-scale interpretation of high-frequency palaeoclimate proxies are discussed. Strictly, given the length of the instrumental data, our results apply to temperature variability on timescales up to, at most, 50 years. Traditional inferences on global mean temperature change based on regional proxies originating around the margins of the northern North Atlantic must be viewed with some caution. Information on temperature change over the oceans, especially the tropical oceans, is an important prerequisite for accurate portrayal of global mean change. Care must be taken when integrating the evidence of different climate proxies to respect the seasonality of the response. Warm-season temperatures are most atypical of the various seasonal averages, especially in the Northern Hemisphere. Inferring annual temperature change on the basis of summer-responsive data is highly questionable.

The Vertical Structure and Development of the ENSO Anomaly Mode during 1979–1989

Abstract The latest two Pacific basinwide warm episodes (1982–83 and 1986–87) exhibit some common features in their development and vertical structure. These features are examined by multivariate empirical orthogonal function analysis of the interannual variability of the ocean-atmosphere system along equatorial Indian and Pacific oceans. The updraft and downdraft branches of the anomalous Walker circulation originate over the western Pacific and the eastern Indian Ocean, respectively. The early development of basinwide warming is characterized by the strengthening of a cross-equatorial low-level southerly component over the eastern Pacific and the enhancement of convection and boundary-layer westerlies over the western Pacific. The structure of the ENSO anomaly mode changes from the cold to the warm phase of the Southern Oscillation. This is attributed to its eastward migration and the intrinsic longitudinal dependence of the vertical structure. The latter results from the east–west contrast of the air–s...

Satellite monitoring of sea surface temperatures off China

Satellite measurements of global sea surface temperatures (SST) have been made since 1982 using the multi-channel radiometers (AVHRR) on NOAA polar orbiting satellites. A four year data set was accumulated at daily intervals and a spatial resolution of about 100 kilometers on an interactive computer system. The time lapse evaluation of the data revealed variations of the SST which were related to coastal and equatorial upwelling events as well as to the pronounced equatorial warming associated with the 1982–1983 El Nino. In the present study, satellite time series are used to describe the annual variability of the SST at selected locations along the coast of China, the Yellow Sea, the Sea of Japan and the Equatorial Indian and Pacific Oceans. Further study of the SST off China using higher resolution satellite data are also described.

Synchronous and time-transgressive Neogene radiolarian datum levels in the Equatorial Indian and Pacific Oceans

Fifty radiolarian events of early Pleistocene and Neogene age were identified in an E-W transect of equatorial DSDP sites, extending from the Gulf of Panama to the western Pacific and eastern Indian Oceans. Our objective was to document the degree of synchroneity or time-transgressiveness of stratigraphically-useful datum levels from this geologic time interval. We restricted our study to low latitudes within which morphological variations of individual taxa are minimal, the total assemblage diversity remains high, and stratigraphic continuity is well-documented by an independent set of criteria. Each of the five sites chosen (503, 573, 289/586, 214) was calibrated to an “absolute” time scale, using a multiple of planktonic foraminiferal, nannofossil, and diatom datum levels which have been independently correlated to the paleomagnetic polarity time scale in piston core material. With these correlations we have assigned “absolute” ages to each radiolarian event, with a precision of 0.1–0.2 m.y. and an accuracy of 0.2–0.4 m.y. On this basis we have classified each of the events as either: (a) synchronous (range of ages <0.4 m.y.); (b) time-transgressive (i.e., range of ages > 1.0 m.y.); and (c) not resolvable (range of ages 0.4–1.0 m.y.). Our results show that, among the synchronous datum levels, a large majority (15 out of 19) are last occurrences. Among those events which are clearly time-transgressive, most are first appearances (10 out of 13). In many instances taxa appear to evolve first in the Indian Ocean, and subsequently in the western and eastern Pacific Ocean. This pattern is particularly unexpected in view of the strong east-to-west zonal flow in equatorial latitudes. Three of the time-transgressive events have been used to define zonal boundaries: the first appearances of Spongaster pentas, Diartus hughesi, and D. petterssoni. Our results suggest that biostratigraphic non-synchroneity may be substantial (i.e., greater than 1 m.y.) within a given latitudinal zone; one would expect this effect to be even more pronounced across oceanographic and climatic gradients. We anticipate that the extent of diachroneity may be comparable for diatom, foraminiferal, and nannofossil datum levels as well. If this proves true, global “time scales” may need to be re-formulated on the basis of a smaller number of demonstrably synchronous events.

Time-Transgressive Neogene Radiolarian Events: Equatorial Indian and Pacific Oceans: ABSTRACT

Fifty radiolarian events (first or last occurrences) of Quaternary and Neogene age were identified in a transect from 5 drill sites (503, 573, 289, 586, 214) in the equatorial Indian and Pacific Oceans, extending from the Panama basin to the 90°E Ridge. Using an absolute chronology for each site based on correlation with the paleomagnetic time scale, we have estimated the degree of synchroneity or time-transgressiveness for each datum. Of those events that appear to be synchronous within the probable uncertainty of our estimate (ca. 0.3 m.y.), 85% are last occurrences. Of those events that are unmistakably time-transgressive (i.e., 1 m.y. or more), 75% are first occurrences in which the taxon evolves earliest in the Indian Ocean and progressively later in the weste n and eastern Pacific. This study, to our knowledge, is the first to document nonsynchroneity of microfossil events within a given latitudinal zone. If this effect proves characteristic of other microfossil groups as well (foraminifera, nannofossils, diatoms), it has important implications for biostratigraphy, geochronology, and plankton evolution. In particular, it suggests a reevaluation of events that presently define zonal boundaries, using precisely dated material, perhaps with the ultimate consequences of favoring last occurrences over first occurrences. The earlier evolution of taxa in the Indian Ocean is particularly unexpected in view of the strong westward zonal flow in low latitudes. End_of_Article - Last_Page 269------------

The occurrence of Oratosquilla investigatoris (Crustacea: Stomatopoda) in the pelagic zone of the Gulf of Aden and the equatorial western Indian Ocean

Surface swarms of the stomatopod Oratosquilla investigatoris (Lloyd, 1907) were observed in the Gulf of Aden and the equatorial western Indian Ocean during 1967. Collections from inshore and offshore swarms were made in both areas, and from demersal trawl catches in the equatorial area. O. investigatoris was also collected from the stomachs of several species of oceanic pelagic and inshore fish from 1965 to 1967, and was also reported in the stomach contents of the lesser frigate bird. Further collections were made from strandings on two oceanic islands in the equatorial area. Indirect observations on the occurrence of the species resulted from increased predation on pelagic longline baits during seasos of apparent abundance of O. investigatoris in the equatorial region. At the surface, predation by the species was observed on fast-swiming fish, and the swimming behaviour was noted. A size range of 6 to 37 mm carapace length (CL) was recorded for the 4000 specimens collected, and there was no size difference between the sexes. Length-frequency analysis of the samples indicated a major mode at 19 to 21 mm CL and an increase in length of 3 mm over 3 months. The sex ratio was weighted in favour of females in the majority of collections. It was concluded that the pelagic swarming of O. investigatoris is an important ecological phenomenon, but not regular in the area, and the factors affecting it could not be deduced from the available data.