Two letter code which defines the ship used.
AA - Aurora Australis
HM - Hakuho Maru
KM - Kaiyo Maru
PS - Polarstern
SH - Shirase
TA - Tangaroa
Time of segment sample in GMT (UTC).
Date of segment sample in GMT (UTC).
A useful field to allow searches by month and for comparison between months,
and also the same month between years.
Another useful field to search for individual years for comparison between
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.
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.
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.
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.
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.
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.