General Information

Ship Code

Two letter code which defines the ship used.

AA - Aurora Australis
HM - Hakuho Maru
KM - Kaiyo Maru
PS - Polarstern
SH - Shirase
TA - Tangaroa

Time

Time of segment sample in GMT (UTC).

Date

Date of segment sample in GMT (UTC).

Month

A useful field to allow searches by month and for comparison between months, and also the same month between years.

Year

Another useful field to search for individual years for comparison between years.

Season

Similar to the Year field, but allows search for data from a particular Antarctic season, based around the austral summer, i.e. the 2002/03 season.

Latitude

Decimal latitude.

Longitude

Decimal longitude.

Segment No.

Individual segment number for each tow, and renumbered for each tow. This field is probably only of value in checking data in the database against the original laboratory counts.

Dist. Nm

The end of each sampling segment is geocoded with latitude and longitude calculated from the one minute time-stamped GPS data. "Dist. Nm" is distance in nautical miles between each segment, which is calculated as the cumulative distance between each 1 minute interval. In theory each segment should be 5 nautical miles exactly but the calculations from the 1 minute intervals is not that accurate, hence the next field "Segment Length". Variation in "Dist. Nm" between segments for a particular tow is thus a calculation artefact. If 10 sec time stamped intervals were used for CPR geocoding program then calculations of "Dist. Nm" would be almost exactly 5 miles with little variation between segments.

Segment length

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 was not always the case with early Aurora Australis data, where it was assumed that each marked segment was 5 nautical miles whereas each tow had subtle variation in silk advancement, depending on 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 have again been recalculated. The last segment of each tow may be less than 5 nautical miles. If the segment is less than 2.5 nautical miles the data are combined with the previous segment and geocoded with the position of the final segment. The combined segment will be between 5 and 7.5 nautical miles. If the last segment is longer than 2.5 nautical miles the segment will remain extant and its length will vary between 2.5 and 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 (12.5 x 12.5 mm).

Volume Filtered = Distance (n miles) x 1852 metres x 0.0125 m2.

A 5 nautical mile segment theoretical represents 1.45 m3.

Species data

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. "Total Abundance" of all zooplankton in a segment has been included as a data field.

Environmental Data

The last four fields are the averaged environmental data for each segment. Three fields, flurometry, salinity and sea water temperature are common to all research vessels used to date. Note: there doesn't seem to be any fluorometry data for Hakuho Maru. The fourth field is light as PAR, which was recorded on all vessels except Shirase, but has been included as a useful parameter to help select data from night and day. Caution: Fluorometry is measured differently on each vessel and are thus not directly comparable between vessels. On Aurora Australis the fluorometry value is arbitrary, although the fluorometer is routine calibrated. On Tangaroa and Kaiyo Maru, fluorometry has been expressed as concentration of chlorophyll a. Salinity on AA has been calculated by thermosalinograph. Temperature on AA 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. Light as PAR is usually recorded as �-Einsteins m-1 s-1.