Terra Nova Bay in Antarctica is a formation region for high-salinity shelf water (HSSW), which is a major source of Antarctic Bottom Water. Here, we analyze spatiotemporal salinity variability in Terra Nova Bay with implications for the local HSSW production. The salinity variations in the Drygalski Basin and eastern Terra Nova Bay near Crary Bank in the Ross Sea were investigated by analyzing hydrographic data from instrumented moorings, vessel-based profiles, and available wind and sea-ice products. Near-bed salinity in the eastern Terra Nova Bay ( ∼ 660 m) and Drygalski Basin (∼ 1200 m) increases each year beginning in September. Significant salinity increases (> 0.04) were observed in 2016 and 2017, which is likely related to active HSSW formation. According to velocity data at identical depths, the salinity increase from September was primarily due to advection of the HSSW originating from the coastal region of the Nansen Ice Shelf. In addition, we show that HSSW can also be formed locally in the upper water column (< 300 m) of the eastern Terra Nova Bay through convection supplied by brine from the surface, which is related to polynya development via winds and ice freezing. While the general consensus is that the salinity of the HSSW was decreasing from 1995 to the late 2000s in the region, the salinity has been increasing since 2016. In 2018, it returned to values comparable to those in the early 2000s.

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c Bacteria of the genus Pseudoalteromonas are ubiquitous in the world's oceans. Marine bacteria have been posited to be associated with a major ancient branch of podoviruses related to T7. Yet, although Pseudoalteromonas phages belonging to the Corticoviridae and the Siphoviridae and prophages belonging to the Myoviridae have been reported, no Pseudoalteromonas podovirus was previously known. Here, a new lytic Pseudoalteromonas marina phage, RIO-1, belonging to the Podoviridae was isolated and characterized with respect to morphology, genomic sequence, and biological properties. Its major encoded proteins were distantly similar to those of T7. The most similar previously sequenced viruses were Pseudomonas phage PA11 and Salinivibrio phage CW02. Whereas many elements of the morphology and gene organization of RIO-1 are similar to those of podoviruses broadly related to T7, RIO-1 conspicuously lacked an RNA polymerase gene. Since definitions of a T7 supergroup have included similarity in the DNA polymerase gene, a detailed phylogenetic analysis was conducted, and two major DNA polymerase clades in Autographivirinae and several structural variants of the polA family represented in podoviruses were found. RIO-1 carries an operon similar to that in a few other podoviruses predicted to specify activities related to ␥-glutamyl amide linkages and/or unusual peptide bonds. Most growth properties of RIO-1 were typical of T7-like phages, except for a long latent period.V iral particles outnumber bacteria in the world's oceans by a factor of about 10:1 and are thought to enforce diversity at the base of the microbiological community by restraining overgrowth of any particularly successful microbial species and returning their biomolecules as nutrients into the water through lysis (1, 2). This role rests critically on a network of specific host-virus interactions. Estimates of viral diversity by metagenomics tend to indicate extraordinarily high numbers of viral species (3-5), yet the total number of sequenced marine bacteriophages as of the last published count (6) was only 17. Current marine phage sequencing initiatives are expected to raise this to only a few hundred.Two of the earliest marine phages genomically characterized were the podoviruses roseophage SIO1 (7) and vibriophage VpV262 (8). These exemplify a group of podoviruses that are vaguely similar to enterobacterial phage T7 but lack the singlechain RNA polymerase and have two converging transcription units rather than one unidirectional transcription unit. It was postulated that this description represented an ancestral phage type present in ancient oceans and widespread descendants would be found in oceanic bacterial species.Pseudoalteromonas is a genus of gammaproteobacteria with many species, all found in marine environments. The genus contains specialists for various marine habitats ranging from sea ice (9) to deep-sea sediments (10). Its species are divided into pigmented and nonpigmented species; the former are known for habitation of marine biofilms and p...