b9e64402-3a54-4ee3-9bbe-51b461c9307c urn:uuid eng UTF-8 nonGeographicDataset nonGeographicDataset 2025-06-23T13:18:25 creation ISO 19115 2016 Subantarctic zone oceanography - SAZ Project 1997-1998 - Oceanography Data b9e64402-3a54-4ee3-9bbe-51b461c9307c The circumpolar Subantarctic Zone (SAZ) is a globally significant region of water mass formation and carbon dioxide uptake from the atmosphere. Here we synthesise the results of nine voyages over 8 years to describe the seasonal variation in mixed layer properties in the SAZ south of Australia for comparison with biogeochemical process studies carried out in late summer (March 1998) as part of the SAZ Project. Winter mixing extends to depths greater than 400 m, resulting in the formation of Subantarctic Mode Water. In summer the mixed layer shoals to 75-100 m, depths which are still sufficiently deep that phytoplankton growth may be light limited. Nitrate and phosphate concentrations are reduced in summer( e.g., nitrate decreases from greater than 15 to less than 5/ micro mol kg- 1) but remain well above limiting levels. Silicate in contrast, is low throughout the year (4/micro mol kg- 1 in winter and less than 2 / micro mol kg- 1 in summer). Water mass properties along a north-south hydrographic section in March 1998 suggest that near-surface waters spread from south to north across the Subantarctic Front (SAF), supplying cool, fresh, nutrient-rich water to the SAZ. As a consequence, the properties of the southern SAZ differ from those farther north: the mixed layer in the south is cooler, fresher, deeper, higher in nutrients, and bounded below by a halocline (rather than by a seasonal thermocline, as in the northern SAZ). The contrast between the northern and southern SAZ persists throughout the year, suggesting the cross-front exchange occurs year-round and likely contributes to the differences in seasonal thermal amplitude and algal biomass accumulation seen in satellite images. Density-compensated horizontal gradients of temperature and salinity are common in the mixed layer of the SAZ and the northern SAF, consistent with the hypothesis that the vigour of lateral mixing in the mixed layer is a strong function of the magnitude of the lateral density gradient. CTD Data are available for access via the provided URL. Data from the following voyages of the Aurora Australis were used: 1991-1992 Voyage 1 1992-1993 Voyage 9 1994-1995 Voyage 4 1994-1995 Voyage 7 1995-1996 Voyage 1 1996-1997 Voyage 1 1997-1998 Voyage 6 {"type": "Point", "coordinates": [141.5, -55.0]} 141.5 141.5 -55.0 -55.0 ACE/CRC AMD AMD/AU CEOS EARTH SCIENCE > OCEANS > OCEAN CIRCULATION > OCEAN MIXED LAYER EARTH SCIENCE > OCEANS > OCEAN CIRCULATION > WATER MASSES EARTH SCIENCE > OCEANS > OCEAN TEMPERATURE > OCEAN MIXED LAYER GEOGRAPHIC REGION > POLAR OCEAN > SOUTHERN OCEAN R/V AA > R/V Aurora Australis SAZ SHIPS GET DATA documentDigital Access CTD data used as part of this project. See Summary for details on which voyages to look at. HTML PROJECT HOME PAGE documentDigital Public information for ASAC project 2256 HTML VIEW RELATED INFORMATION documentDigital Download point for the referenced publication HTML VIEW RELATED INFORMATION documentDigital Citation reference for this metadata record and dataset HTML Creative Commons by Attribution logo documentDigital PNG