Introduction

This programme involved a five-person party working from the fast ice in the southwestern Ross Sea. Sea floor samples were taken along eight shore-normal transects from Blue Glacier to Tripp Bay and at Cape Armitage (Figure 1). The transects represent a range of coastal types (exposed to embayed) with a variety of substrates, including bedrock, gravel, sand, mud and sponge mat.

We travelled on the fast sea ice by D-3 tractor pulling three Cantago sledges and used a Grizzly toboggan for bathymetry surveys and route finding. The first sledge was set up as a sea ice drilling platform, with hydrographic winch, drill and drill mast, grab, fuel and tools. The second sledge carried the NZ-1 wannigan, which is fitted with bunks, table, desk and small kitchen. This was used as a laboratory for mixing preservative for the sediment samples, as a dry lab for the IBM PC, used for programming and interrogating the S4 current meter, and as a kitchen and working area. The third sledge carried the remaining cargo, such as tents, personal baggage, the Grizzly when not in use, further fuel and miscellaneous cargo. A VUW ski trailer for use with the Grizzly was towed last.

Figure 1. Map showing the eight nearshore seafloor sampling transects.

1. Explorers Cove New Harbour
2. Cape Bernacchi
3. Cape Roberts
4. Tripp Island
5. Gregory Island
6. Dunlop Island
7. Blue Glacier
8. Cape Armitage

Sea floor sediment sampling

At each of the eight sampling transects, a bathymetric survey was carried out to determine the slope and topography of the sea floor (Figure 2). This was carried out by drilling 4-inch holes in the sea ice and using an echo sounder to measure the water depth by passing the 200 kHz transducer through the hole below the sea ice.

The sampling strategy was designed so that sediment was recovered from similar depths at each transect. The depth zones sampled included a sea ice scoured zone, from 0 to 5-10 m, a possible wave influenced zone, from 5 to 20 m, and a non-wave influenced zone, from 20 to 100 m. The effects of bottom currents, which are depth and site specific, were also considered in the sampling strategy.

The sediment samples were recovered with a modified Shipek grab designed and built at Victoria University. The grab has two interchangeable 180×180 mm hemicylindrical buckets that take a 90 mm deep scoop of the sea floor. These samples were first photographed and described intact, then split into portions and preserved in formalyn. A subsample of each grab will be preserved as an archive specimen, and another split will be used for foraminiferal work and grain size analysis.

Results

Several areas of exposed bedrock were identified during the sampling programme. These sites had very little sediment cover, and are generally in shallow water. They include exposed capes and steeply dipping (17°) sea floor. Tripp Island and Gregory Island exhibit this sort of submarine topography (Figure 2). The bedrock surfaces extend deeper than sea ice influences, so other factors must be responsible for the lack of sediment. These include glacial ice scouring, non-deposition at the present time and strong current activity.

Intermediately sloping sea floor localities include Cape Roberts, Dunlop Island and Cape Bernacchi (Figure 2). These have exposed bedrock from 0 m to 10 or 20 m, then gravel which grades to muddy sand at about 100 m.

Beach-type coastal topography is found at Explorers Cove (New Harbour, Figure 2) and Blue Glacier. These areas have gravelly sand at 0 m with sediment fining into the deeper water. Blue Glacier (0 to 40 m depth) is a moraine remnant, presumably ice cored, with a slope of 15°. Further offshore the slope lessens to 3°.

Cape Armitage, on Ross Island (Figure 2) has a substrate of volcanic scoria. We found this transect to be strongly influenced by sea floor anchor ice formation in water to 11 m depth, and a very strong current (75 cm/sec) regime.

Figure 2. Bathymetry and sediment distribution along each of the eight sampling transects. Spot depths and sample sites (arrows) are shown for each transect. The major types of biota recovered are shown for each sample at the left side of each transect.

Figure 2. Bathymetry and sediment distribution along each of the eight sampling transects. Spot depths and sample sites (arrows) are shown for each transect. The major types of biota recovered are shown for each sample at the left side of each transect.

Macro-flora/fauna

Invertebrate animals and some plant materials were collected during the grab sampling programme. Different species of animals and plants have certain substrate preferences. Echinoids and some pectens were found on the bedrock surfaces (Figure 2). Pectens were also found in shallow water on sandy mud bottoms. Live sponges and sponge mat (disaggregated dead siliceous sponges) were found from 50 to 100 m and probably continue deeper in certain areas off shore (Ward 1984). Large (5 cm high) reddish algae was found only in the northern areas, as isolated specimens, the algae occurred in water less than 50 m deep, on bedrock or coarse sediment. Its distribution could be influenced by proximity to more open water and Ross Sea circulation patterns.

Micro-algae

Diatoms, often comprising biogenic mud of an olive-green colour, were present entrapped in sponge mat and in deeper water basins, especially in areas of low current activity, such as Tripp Bay. Specimens of diatom ooze were collected for S216.

Current Measurements

Water current measurements were made this season at the 100 m site of most of our coastal transects using a newly purchased InterOcean S4 electromagnetic current meter. This current meter is housed in a 250 mm diameter sphere, has no moving parts, records data internally and is ideal for deployment through our 300 mm diameter access holes in the sea ice. The instrument was programmed and interrogated with an IBM PC operated in the warm environment of the wannigan (NZ-1).

Two modes of deployment were used at the 100 m deep sites. Water column profiling measurements were made while either raising or lowering the current meter with our new hydraulically controlled hydrographic winch. Short term (12-24 hours) fixed-mooring measurements were also made by suspending the current meter on the winch wire 1.5 m ± 0.5 m above the sea floor. The height of the instrument above the sea floor could not be fixed precisely using this method of deployment because of the approximately 1 m tidal rise and fall of the sea ice platform.

Profiles and short term deployments were also made in central Granite Harbour near the MacKay Glacier Tongue and in central New Harbour (S216 Trap Site). This data will be used for planning a longer term deployment (2 months) proposed for the 1988-1989 season.

Examples of results from profiles and stationary moorings are presented in Figures 3 and 4. The highest speed measured along the southwestern Ross Sea coast page 9

Figure 3. Current measurements at Gregory Island (98 m site).

A.	Profile showing consistent speed and direction through most of the water column.
B.	Stationary mooring 1-2 m above the sea floor (13 hour 48 min record). Note the increase in speed as high tide is approached and progressive change in direction from southward flow to a northward flow. The strongest flow is to the north.

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Figure 4. Current measurements at Cape Armitage (90 m site).

A.	26 hour deployment 1-2 m above the sea floor showing currents up to 75 cm/sec were recorded flowing to 150° true (SSE). Lower velocity currents up to 25 cm/sec flowing to 250° true (WSW).
B.	Profile about 2 hours after the end of record above (A). A steady flow of 75 cm/sec to 150° T is shown for most of the water column.

page 11 was 25 to 30 cm/sec at Gregory Island (Figure 3). The lowest current speed along this coast was 12 cm/sec, measured at Blue Glacier. Current directions are parallel to the coast and change by 180° during the tidal cycle. Speeds measured in embayed areas such as New Harbour, Granite Harbour and Tripp Bay are lower (less than 12 cm/sec) than those on the exposed coast. Current direction at Cape Armitage (Figure 4) also changes with the tidal period, with speeds up to 75 cm/sec, and were the highest measured this season.

Water Sampling

Water samples for oxygen and carbon isotope analyses by Dr Enriqueta Barrera, Ohio State University, were taken at the 100 m site of each of the eight transects. Samples were collected using a small Niskin bottle deployed 10 m below the sea ice and 5 m above the sea floor at each site. Subsamples were measured for pH within 2 hours of collection. We had hoped to collect water samples for this study from previous 1981 sea floor sample sites, but the lack of sea ice cover in the central part of McMurdo Sound made this impossible this season.

Tripp Bay Bathymetry

A spot depth bathymetry survey was begun this season in Tripp Bay in association with Dr Robert Dunbar of Rice University, Texas (S216). The aim of the survey was to compare Tripp Bay with Granite Harbour and identify any deep basins which could be accumulating diatom-rich sediment as in Granite Harbour. We were also interested in this area as a site which is isolated from the influence of McMurdo Sound oceanographic circulation.

The maximum depth recorded this season was 550 m in the area south of Tripp Bay Glacier Tongue (Figure 1). Further measurements are still required to the east and north of the glacier tongue to complete the survey. The New Zealand survey party, K191, surveyed all flagged bathymetric locations so an accurate map of the sea floor in this area can eventually be constructed.