Southern Coral Sea Research Articles

The mid‐Pleistocene transition in the subtropical southwest Pacific

Reconstructions of subtropical southwest Pacific climate variability over the Pleistocene were derived from coupled planktic foraminiferal δ18O‐Mg/Ca measurements taken from a southern Coral Sea sediment core. A clear shift from ∼40 kyr to ∼100 kyr modes of reconstructed glacial‐interglacial sea surface temperature (SST) variability is seen over the mid‐Pleistocene transition, and these fluctuations are shown to have remained coherent with the orbital obliquity cycle across the transition. The likely origin of this strong obliquity signal in subtropical southwest Pacific SST is shown to be the southern high latitudes, and comparison with existing SST reconstructions from the equatorial Pacific is consistent with the communication of the signal occurring principally by greenhouse gas forcing. In contrast to the SST reconstruction, regional hydrological cycle variability (based on the calculated local component of δ18Osw change) does not show significant coherence with obliquity after ∼1000 ka. The decoupling of the SST and hydrological cycle responses over the mid‐Pleistocene transition allows constraints to be placed on the evolution and extent of orbitally paced fluctuations within the coupled low‐latitude ocean‐atmosphere system.

Composition and distribution of deep-sea benthic invertebrate megafauna on the Lord Howe Rise and Norfolk Ridge, southwest Pacific Ocean

The deep-sea biodiversity of the Lord Howe Rise and Norfolk Ridge – two complex submarine features that extend in a north-south direction either side of a deep basin within the northern Tasman Sea and southern Coral Sea – was sampled in 2003 for the first time on a broad regional scale. The total of 1313 megabenthic invertebrate species from 17 higher order taxa collected between 100 and 1800 m depths showed faunal diversity and novelty was high. Only 256 of these species were named, and 10% of these were described as a result of this survey; 78% are un-named and believed to be mostly new species. Of the 1253 species included in quantitative analyses, most appeared to be rare – 85% were only found once. This indicates intra-regional endemism may be high, but undersampling is also likely. Species accumulation curves confirm that many additional species remain to be collected. There was high regional-scale spatial heterogeneity in species distribution patterns which appeared to be influenced by hydrographic patterns and feature-scale topography, and to a lesser extent by seabed type. Depth and oxygen concentration (correlated with depth) had most influence on distribution patterns of fauna, with assemblages identified from three depth-zones: 100–400 m (deep continental shelf and shelf edge), 400–700 m (upper continental slope) and >700 m (mid-continental slope). In the shallowest depth zone, there were north-south (latitudinal) patterns in invertebrate assemblages that appeared to be influenced by water mass distribution. Species overlap was higher in the south than the north, probably due to the Tasman Front forming a hydrographic connection between the southern parts of the Rise and the Ridge at shallower depths. At depths >700 m, the absence of a latitudinal pattern in assemblage structure was attributed to the continuity of Antarctic Intermediate Water in the study area. Differentiation of two assemblages in sled samples from the >700 m depth zone, as well as some patterns of diversity of large sessile fauna between sub-regions within the study area, suggested a relationship with bottom type but this was not fully analysed. While providing a major increase in scientific knowledge of marine biodiversity in deep waters of the Coral and Tasman Seas, these results also highlighted the paucity of biogeographical knowledge that exists for the area. Some science advances needed to inform national and international conservation plans currently under development are identified. They include taxonomic standardisation at a regional-scale (Australia, New Zealand and New Caledonia) for informative higher level taxa, and some additional surveys of selected areas and seabed features, including off northeastern Australia.

Contrasting local retention and cross-shore transports of the East Australian Current and the Leeuwin Current and their relative influences on the life histories of small pelagic fishes

Transport between shelf and offshore environments supports a significant proportion of ocean primary productivity and is critical to the life cycle of many marine species. While fundamental differences in the underlying dynamics of eastern and western boundary currents have been recognized and studied for more than half a century, the implications for physical dispersal rates have received much less attention. In this study we explore how Australia’s two major boundary current systems, the East Australian Current and the Leeuwin Current, differ in their local retention and cross-shore transports in the upper water column and how these differences favor contrasting life histories of small pelagic fishes. The results suggest that the East Australian Current forms a partial barrier to onshore transport, but is effective in entraining shelf waters and transporting them offshore, particularly in the region where the current separates from the coast. Blue mackerel ( Scomber australasicus) spawn on the outer-shelf in this separation region and may thereby maximize the dispersion of eggs and larvae in the mainly oligotrophic waters of the southern Coral Sea. In contrast, the Leeuwin Current system promotes onshore transport through the combined effects of mean onshore flow and eddy-induced mixing. In the Great Australian Bight, sardine ( Sardinops sagax) and anchovy ( Engraulis australis) may exploit the high coastal retention of the Leeuwin Current system by spawning on the inner-shelf during summer when the current is weakest and winds assist retention and enhance production through local upwelling.

The birds of the Southern Coral Sea including observation by HMS Herald in 1858-60

The birds of the Southern Coral Sea including observation by HMS Herald in 1858-60

Mesoscale circulation features of the great barrier reef region inferred from NOAA satellite imagery

The commissioning of a NOAA satellite receiving station at Townsville in North Queensland in 1988 greatly expanded the A VHRR coverage of the northeast Australian region to include the entire Great Barrier Reef system and marginal seas. Selected imagery from this and a southern station installed previously at Aspendale, Victoria provide a valuable new perspective on oceanographic phenomena occurring in this ecologically significant region. This perspective could not be attained using conventional ship-board and in situ oceanographic sampling techniques. A rich spectrum of mesoscale oceanographic features is revealed in the analyzed imagery, and various features such as western boundary current meanders, frontal shear waves, eddies, and jets are described. The temporal and spatial variability of these features appears strongly linked to that of the larger-scale Coral Sea current circulation. Several of the features identified are unique to the region; others resemble features observed in other western boundary current systems, but are significantly modified by the complex regional topography, and by the presence of the Great Barrier Reef (GBR). Evidence has been found for a number of processes which have significant implications for the origin and maintenance of GBR ecosystems, including shelf edge exchange processes, stratified slope water intrusions onto the shelf, and boundary layer mixing around reefs. Such processes provide a mechanism for injection of cool nutrient-rich waters into the reef matrix. The imagery provides a clear picture of a well-organized, but spatially complex, frontal system existing in the southern Coral Sea, which is associated with enhanced commercial and recreational fishing activity in the region. The AVHRR imagery has thus proven to be a valuable tool for spatial mapping of oceanographic features throughout the GBR region, for hypothesis formation in dynamical and modeling studies, and for ship-board reconnaissance operations.

Spatial Variability of Recent Otolith Growth and RNA Indices in Pelagic Juvenile Diaphus kapalae (Myctophidae): an Effect of Flow Disturbance near an Island?

In February 1993, the pelagic juvenile myctophid Diaphus kapalae was sampled with a neuston net in the southern Coral Sea in a region of flow disturbance north of Cato Reef, and to the east in the free stream (northerly flow at 30 cm s-1). There was no significant difference in the size (11-16 mm SL) or age (45-74 days after hatching) between the two regions. Recent growth indices derived from the width of the peripheral daily growth increments (~10 μm each) revealed enhanced otolith growth 38 km downstream and up to 4 days before capture. No significant difference was found for times longer than a week before capture, consistent with fluctuation of the wake indicated from current-meter data. Daily increment formation was confirmed by marginal increment analysis. Recent otolith growth was correlated with the RNA content adjusted by dry weight, which also revealed significantly higher condition in the wake region. Recent growth was correlated with microzooplankton biomass, recorded with an optical plankton counter.

Patterns of disseminule dispersal by drift in the southern Coral Sea

Abstract Assemblages of drift disseminules are described from beaches of cays in the southern Coral Sea. Most disseminule taxa are widespread, but their proportions in assemblages vary. The patterns are concordant with prevailing winds and currents, and suggest that disseminules drift towards the southern Great Barrier Reef area in distinct streams, from the east (Fiji, Vanuatu, New Caledonia, via the Chesterfield Reefs area) and from the north or northeast (possibly New Guinea and/or the Solomon Islands). Australia-derived disseminules make a minor contribution to assemblages on cays on the southern Great Barrier Reef but none further east. Human-derived flotsam increases in areas west of Chesterfield Reefs.

Estimates of sea surface temperature in the Coral Sea at the Last Glacial Maximum

The CLIMAP [1981] reconstruction of the Coral Sea found relatively little cooling (2°C) in the low latitudes (10°S) but a warming off Australia at about 25°S. The small low‐latitude changes are of interest because terrestrial pollen and snowline data from the New Guinea highlands imply that surface temperatures may have been 6° to 9°C colder at the last glacial maximum (LGM). The purpose of this paper is to evaluate these conclusions on the basis of additional core sites, new oxygen isotope stratigraphy, and new sea surface temperature (SST) estimates using the modern analog technique (MAT). In the northern Coral Sea, planktonic foraminifer assemblages consist of tropical‐subtropical species that show little change over the past 20 kyr. Quantitative estimates of SST using the modern analog technique (MAT) confirm the CLIMAP [1981] conclusion that little or no temperature change occurred in this tropical region at the LGM, thus reinforcing the conflict with terrestrial evidence. In the southern region (25°S), two cores indicate that foraminifer faunas became more subtropical at the LGM. The MAT estimates for the LGM are 3° to 4°C colder than modern, producing a steeper thermal gradient in the southern Coral Sea. These data remove the warm SST anomaly along the eastern coast of Australia and indicate that during the LGM, cool high‐ latitude waters were displaced northward along the coast of Australia into the southern Coral Sea.

マカジキに関する水産海洋学的研究-II

The distribution of striped marlin, Tetrapturus audax, in the Pacific Ocean is known to form a horseshoe-shaped pattern, extending both ways to the northwestern and southwestern Pacific with the eastern tropical Pacific the apex. The southern Coral Sea fishing ground which is located in the western extremity of the South Pacific Ocean is known to be an important spawning ground for the species. To study the spawning stock, the author examined the fishing season, the shifts in fishing grounds, and the movement pattern of the striped marlin through the analysis of data obtained from the tuna longline fishery. The results were as follows: 1. The catch rate (catch per 100hooks) of striped marlin in the southern Coral Sea usually begins to increase in September, and the fishing season continues until January. The fishing season peaks between November and December. 2. The productive fishing grounds in November and December are located in the area from lat. 20°-30°S, long. 154°-160°E, and also along lat. 20°S in waters off the northwestern coast of New Caledonia. 3. Based on the movement of the fishing grounds, it can be surmised that the striped marlin occurring in the southern Coral Sea have their origin in the eastern Pacific Ocean. In September through the area bounded by lat. 25°-25°S, long. 170°W-180° and later through the area bounded by lat. 25°-30°S, long. 170°E-180°. They subsequently congregate around lat. 25°-30°S, long. 160°E. The movement in the southern Coral Sea is towards the north beginning in October, and southward beginning in January.