Deep circulation in the Lau Basin and Havre Trough of the western South Pacific Ocean from floats and hydrography

A system of meridional ridges in the western South Pacific Ocean frame the Lau Basin and Havre Trough, and form a barrier to direct communication between the far western South Pacific basins and the interior South Pacific Ocean. The eastern side of this system comprises the Tonga and Kermadec Ridges, the location of the main deep western boundary current entering the Pacific Ocean. Observations from floats released in the Lau Basin as part of the RIDGE2000 program suggested the presence of a western boundary current along the Lau Ridge exiting into the North Fiji Basin. Those observations, together with Argo sub-surface float data and repeat hydrographic sections, confirm and expand the boundary current observations along the Lau Ridge throughout the Lau Basin and into the Havre Trough, along the Colville Ridge. The observations also reveal two previously unrecognized westward flowing jets bisecting the Lau Basin and Havre Trough. Using an extension to the classic Stommel-Arons abyssal circulation model, the predicted strength and location of these boundary currents and their bifurcation is compared with the float observations. The model provides a simplified view of the dynamics controlling the boundary current structure in the deep basins. A comparison of transport within the western boundary current derived from float data, hydrographic sections, and the idealized analytical model indicates that roughly 4 Sv (below 1,000 db) is transported northward through the Lau Basin, exiting into the North Fiji Basin.

A new species of hydrothermal vent stalked barnacle Vulcanolepas (Scalpelliforms: Eolepadidae) from the North Fiji Basin, Southwestern Pacific Ocean

A new species of eolepadid stalked barnacle, Vulcanolepas fijiensis sp. nov., was collected from a hydrothermal vent in the North Fiji Basin, Southwestern Pacific Ocean, at a depth of 1988 m. Based on morphological characteristics, this new species was distinguished from its relatives, V. osheai Buckeridge, 2000, V. parensis Southward, 2005, V. scotiaensis Buckeridge, Linse & Jackson, 2013, and V. buckeridgei Chan & Chang, 2018. Based on morphological characteristics, Vulcanolepas species are divided mainly into two groups by the size of the first mandibular tooth; the first group has a large mandibular first tooth (V. parensis, V. scotiaensis, and V. fijiensis sp. nov., the second a small mandibular first tooth (V. osheai and V. buckeridgei). The new species can be easily distinguished from V. parensis and V. scotiaensis by the length ratio of antenniform segments to robust segments of the rami of cirrus I. Vulcanolepas fijiensis sp. nov. also differs from V. parensis by the length ratio of the penis and cirrus VI (1/10 vs 1/4), and the extension the carinal apex to the tergum (extended vs not extended). Additionally, the sequence divergence of the cytochrome c oxidase 1 gene between V. fijiensis sp. nov. and the other neolepadid species (except V. parensis from its original locations) ranged from 4.2% to 14.0%. In a neighbor-joining tree, V. fijiensis sp. nov. formed an independent branch. These results infer that V. fijiensis sp. nov. is a new species, distinct from the other known neolepadids.

A new species of Archinome (Polychaeta: Archinomidae) from hydrothermal vents on the Pacific–Antarctic Ridge 37°S

Archinome storchi sp. nov. is described as the second species of the family Archinomidae. The specimens were collected from a hydrothermal vent site in 2212 m depth on the Pacific–Antarctic Ridge at 37° S. It differs from Archinome rosacea mainly in the position of the anus, the first appearance of branchiae and the length of the nuchal cirrus. Additional specimens of A. rosacea collected from hydrothermal vent locations in the North Fiji Basin and on the Mid-Atlantic Ridge were used for morphological comparison. A synoptic table of characters is given for A. rosacea and A. storchi sp. nov. together with a list of records for Archinomidae compiled from the literature.