This dataset contains results from Continuous Plankton Recorder (CPR) surveys in the Southern Ocean. When the opportunity arises, zooplankton species, numbers and abundance data are recorded on a continuous basis as vessels steam through the area between Australia and Antarctica, including Heard and Macquarie Islands. Observations have been made since June 1990 and are ongoing. Obviously the observations are not continuous over the region with time.
Many of the original SO-CPR logbooks from the various voyages have also been scanned, and are available via the Australian Antarctic Data Centre's Reports Register.
Zooplankton have been identified to lowest possible taxon, usually species, and counted for each segment. For copepods, copepodites and for some species nauplii (e.g. Rhincalanus gigas) have been counted separately, and for euphausiids, naupliar, calyptopis and furcilia developmental stages are identified.
The fields in this dataset are:
Tow_number - the CPR tow number
Ship_name - the name of the ship on which the tow was conducted
Season - two-year Antarctic season based around the austral summer, e.g. '2000-01' runs from July 2000 to June 2001
Latitude - the decimal latitude of the segment sample
Longitude - the decimal longitude of the segment sample
Observation_date - UTC date and time of the segment sample in ISO8601 format (yyyy-mm-ddTHH:MMZ)
Observation_date_year - the observation date year
Observation_date_month - the observation date month
Observation_date_day - the observation date day
Observation_date_hour - the observation date hour
Observation_date_minute - the observation date minute
Observation_date_time_zone - the observation date time zone (0=UTC)
Segment_number - the individual segment number within each tow
Segment_length - the distance travelled by the CPR during this segment (nautical miles). This is the true segment length as used in the Geocoding program used to cut the silk, and to calculate positions and average environmental data for each segment. In theory, all segments are 5 nautical miles long. However, this wasn't always the case with early Aurora Australis tows, where it was assumed that each marked segment was 5 nautical miles whereas each tow had subtle variations in silk advancement, depending on the wear of the cassette or travel with or against a current. True segment length has since been recalculated. At other times, some silks have been incorrectly cut and the true length has again been recalculated. The last segment of each tow may be less than 5 nautical miles. This field can be used to standardise species counts to say 5 nautical miles or to a theoretical volume filtered by multiplying the distance travelled by aperture area (12.7 x 12.7 mm): Volume Filtered = Distance (n miles) x 1852 metres x 0.0127^2. A 5 nautical mile segment theoretically represents 1.49 m^3.
Total_abundance - total count of all zooplankton in a segment
Phytoplankton_colour_index - visual estimation of the green colour of the silk mesh. Values are 'No Colour', 'Very Pale Green', 'Pale Green', or 'Green'. This colouration is due to the green chlorophyll pigments derived from chloroplasts of intact and broken cells and small unarmoured flagellates. It may provide an indicator of phytoplankton standing stock, although in the Southern Ocean there are some diatoms that are quite common on the silks but as they have very low amounts of chlorophyll the colour doesn't register in the PCI analysis.
Fluorescence - water fluoresence measured by the vessel, averaged for the segment (arbitrary units). See Quality notes for more information.
Salinity - water salinity measured by the vessel, averaged for the segment (psu). See Quality notes for more information.
Water_temperature - water temperature measured by the vessel (degrees Celsius). See Quality notes for more information.
Photosynthetically_active_radiation - photosynthetically active radiation measured by the vessel (micro-Einsteins m-2 s-1). This is not available on some vessels but has been included as a useful parameter to help differentiate data from night and day.
The remaining fields ('Abylidae' through to 'Vibilia_sp') are zooplankton taxon names. The entries in these columns are the counts of each taxon in the segment.
Caution: Fluorometry is measured differently on each vessel and are thus not directly comparable between vessels. Most values come from Turner fluorometers. The Aurora Australis has a Turner TD10, and the units are arbitrary even though the fluorometer is routinely calibrated. Further, a value of 200 on one voyage is not necessarily the same as 200 on another voyage, even with daily calibration and cleaning of the sensor. The fluorometry values are really only of value within a voyage in as much that 200 is double the fluorescence activity of 100. On Tangaroa and Kaiyo Maru, fluorometry has been expressed as a concentration of chlorophyll a. There doesn't seem to be any fluorometry data for Hakuho Maru.
Notes on salinity:
The salinity measurement comes from the various thermosalinograph units mounted in the underway systems of the ships. Salinity on the Aurora Australis has been calculated by thermosalinograph. Salinity values are expressed in practical salinity units.
Notes on water temperature: Temperature on the Aurora Australis is measured by a high resolution thyristor near the entrance of a dedicated seawater line, to avoid the problems of heating of the water in by the ship as it passes through pipes. Again the data may not be fully comparable with other vessels.
Notes on segment length:
The end of each sampling segment is geocoded with latitude and longitude calculated from the one minute time-stamped GPS data. 'Segment Length' is the distance in nautical miles for each segment, which is calculated as the cumulative distance between each 1 minute interval. In theory, all segments are 5 nautical miles long. However, this wasn't always the case with early RSV Aurora Australis tows, where it was assumed that the silks advanced at a predetermined rate of 1 cm per nautical mile, whereas each tow had subtle variations in silk advancement, depending on local condition, e.g. whether the CPR was travelling with or against a current. True segment length has since been recalculated. At other times, some silks have been incorrectly cut and the true length has again been recalculated. The last segment of each tow is rarely exactly 5 nautical miles. It is usually less. In this situation we apply the following rule: if the last segment is longer than 2.5 nautical miles it remains as a segment in its own right and can be between 2.5 and 4.99 nautical miles, whereas if it is less than 2.5 it is added to the penultimate segment making the last segment 5 to 7.49 nautical miles. Users of the data can elect to dismiss the last segment. The 'Segment Length' field can be used to standardise species counts. Dividing abundance values by the respective segment length will produce numbers per nautical mile, which is equivalent to a volume of water filtered of 0.30 cubic metres (1 nautical mile is 1852 m, multiplied by the aperture area of 12.7 x 12.7 mm). A 5 nautical segment is equivalent to 1.49 cubic metres.