VAN AMSTERDAM. (project 101A) S. van der Spoel. Abstract. The present list comprises the data on all. discrete depth samples and open

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1 May May Bulletin Zoologisch Museum VAN AMSTERDAM Vol. 8 No List of discrete depth samples and open net hauls of the Amsterdam Mid North Atlantic Plankton Expedition 1980 (project 101A) S. van der Spoel Abstract The technical details and hydrographical data of the hauls with open nets and openingandclosing made nets, during the Amsterdam Mid North Atlantic Plankton Expedition are given together with the general conditions during the sampling period April 11 2, A and temperature salinity profile between 55 and 25 N to a depth of 2000 m are presented with ten XBT records. INTRODUCTION The present list comprises the data on all discrete depth samples and open net hauls made The research programme 101A of the Institute of in thç period April 11 2, 1980 in the Mid Taxonomic Zoology, University of Amsterdam, primarily aims at elucidating the patterns North Atlantic between 55 and 24 N. The discrete depth samples were made between 30 m and of latitudinal diversity, taxonomic variation below 1200 m depth with the Rectangular Midwater the species level, vertical variation and the Trawl (RMT1+8) developed by the Institute of interaction of climate, hydrographie features, Océanographie Sciences, Wormley, Great Britain. ecology and morphological variation of marine The open net hauls were made with an open one plankton. square metre Rectangular Midwater Trawl (RMTl) and with an open ringnet in the upper 150 metres. ') AMNAPE, Proj. 101A, rep. no. 1, supported by a grant of the Netherlands Ministry of Educa In addition to these samples, microplankton tion and Sciences pump samples were taken, temperature, daylight

2 Position Fig. 1a of the stations with a diagrammatic representation of surface currents (arrows) and the polar front (double line).

3 Position Temperature Fig. 1b of the stations and hauls in Fig. 2 ( C) profile of the cruise a vertical profile, giving the open between 55 and 24 N. Vertical lines ingclosing net samples (solid) and open net hauls (open). indicate XBT and net monitor temperatures, with their numbers along the yaxis, depth in metres along xaxis.

Sea 4 Fig. 3 surface temperatures ( C) in the area investigated, from the left to the right on 15, 22 and 29 April, 1980 based on NOAA satellite measurements (courtesy of the U.S. Dept.

4 Sea 4 Fig. 3 surface temperatures ( C) in the area investigated, from the left to the right on 15, 22 and 29 April, 1980 based on NOAA satellite measurements (courtesy of the U.S. Dept. Commerce, National Oceanographie and Atmospheric Administration). fluctuations and DSL migration were measured, based on NOAA satellite data, for three days and bird countings were carried out; these re during the expedition, viz. 15, 22 and 29 sults will be published elsewhere. April, 1Ç80. The diagrammatic salinity profile The discrete depth samples and open net in fig. 4 is composed from temperature and hauls are given in fig. la and, except for the sound velocity records which do not provide test stations 9 and 27, also in fig. lb. The sufficiently accurate data to produce here more stations 15 concern the test cruise to the Bay than the 36 / 00 and 349 / 00 isohalines. of Biscay the data of which will be published by Heyman (in press). All samples were roughly sorted aboard ship, fixed and preserved in the COLLECTING METHODS most appropriate way according to the animal groups concerned. Alcohol 70 / oo, propylene phenoxetol, formalin \ % and formalin 2 % in sea The Rectangular Midwater Trawl RMT1+8 is a combined opening and closing net composed of a water were the most frequently used fixatives large net with an effective mouth area of 8 m 2 (Heyman, in press). All material is preserved (the RMT8) and a smaller one on top with an 2 effective mouth area of 0.8 m (the RMT1 ). The in the Institute of Taxonomic Zoology, Amsterdam. RMT1 is made of nylon sifting cloth with a mesh The temperature measurements made with XBTs size of 0.32 mm throughout. The RMT8 is made of and with the RMT net monitor system form the nylon sifting cloth with a mesh size of 4.5 nm basis of the temperature profile in fig. 2. In and in the cod end of 1.0 mm. Shipspeed during fig. 3 sea surface temperatures are shown, fishing was kept as close to two knots as

5 Salinity 5 possible. Fundamentally, a sampling scheme was maintained in which hauls between 50100, , , , and m depth were made. Fishing was carried out obliquely downwards through the layers sampled. The net monitor provides accurate data on depth, temperature and flow during fishing. For a full description of the nets and their behaviour one is referred to Baker & al. (1973) and Roe & al. (1980). The open Rectangular Midwater Trawl (RMT1) was the same net as the one used in the RMT1+8 combination. The ringnet, designed for this cruise, has a circular mouth opening of 0.78 m and is made 2 of a conical sifting cloth with a mesh size of 0.18 mm, the sifting surface is 2.8m, cod end included. It is towed through the water at a speed of ca 2 knots with 80 or 3 metres wire out. This method results in an estimated fishing depth of SO and 180 metres respectively, and an effective mouth area of ca 0.55 m. In 2 some of the hauls the normal cod end of 0.18 mm mesh size was replaced by a RMT1 liner with mesh size 0.32 mm. At stations 919 the open hauls were made from the stern of the ship and the RMT1+8 was lowered from the main working deck at starboard, at stations 2027 the RMT1+8 and the open RMT1 were handled from the stern and the open ringnets were lowered from the main working deck at starboard. Slight differences in behaviour of the nets are to be expected resulting from these various ways of operation, but any influence on the catching rate is presumed to be absent. Nine hauls were made at dawn, 69 in the daytime, 14 at dusk and 40 during the night, making a total of 132 hauls; details are given in table I. CONDITIONS From the temperature and salinity data presented in figs. 13 the different water masses can Fig. 4 profile of the cruise between 55 and 24 N based on sound velocity be roughly deduced. measurements, made available by courte Between 55 and 53 N the Polar thermal fronts are found; the most southern frontal of the sy Hydrographic Office of the Royal Dutch in Navy, relation to temperature, depth in metres. phenomenon is found at 53 N. The. water north of

6 Fig. 5 Ten curves from XBTs temperature taken at the most characteristic localities. a) N W, 15IV1980, h., near stat. 11; isothermal Subarctic Waters; b) N W, 15IV1980, h., stat. 11; in thermal front; c) N W, 16IV1980, h., stat. 12; with cold surface layer; d) N W, 16IV1980, 1435 h., between stats 12 and 13; surface layers still isothermal; e) N W, 20IV1980, 0535 h., near stat. 16; surface layers still isothermal; f) N W, 20IV1980, h., stat. 16; influence ofnorth Atlantic Current, southern branches; g) N W, 25IV1980, near h., stat. 20; surface layers still isothermal; h) N W, 26IV1980, h., stat. 21; developing shallow thermocline; j) N W, 27IV1980, h., stat. 22; with surface water thermocline; k) N W, 01V1980, 0545 h., stat. 26; with deeper thermoclines.

7 7 53 N can be considered Subarctic Water. Near the Canary Current do not differ essentially 51 N the North Atlantic Current influences the from those at station 26. temperature profile. A southward running branch A few simple Secchidisc readings were made of the North Atlantic Current, found near 42 N, with a white disc with a diameter of 91 cm The is bordered at its northern side by a weak results are given in table II. thermal front. Warm Temperate Water is found between 50 and 42 N. A subtropical convergence cannot be indicated. The North Atlantic Central ACKNOWLEDGEMENTS Water reaches 38 N. The Sargasso Sea Water is considered to occur between 27 and 40 N. South of 27 N the influence of the Canary Current The author, who was responsible for the expedition, expresses his sincere thanks to the Royal Water is traceable. Dutch Navy for help during the organisation and Below a depth of 500 m the Antarctic and more especially to commander and crew of the Arctic Intermediate Waters are found. The ris ocean research vessel H.M.S. "Tydeman", for ing of the 34.9 /oo isohaline near 36 N proba their neverfailing efforts during the cruise. The technical advice and the final supplying of bly indicates the presence of a tongue of Antarctic Intermediate Water. A core of Mediterranean Water, expected at depths of m, the fishing gear by the Institute of Océanographie Sciences, Godalming, Great Britain, were is not found, though between 38 and 42 N the of basic importance and deeply felt gratitude isotherm bent downwards, probably due to this is expressed to the staff of the I.O.S. for water mass. The high salinity core at moderate this kind assistance. depth between 43 and 51 N is too large to be considered to represent Mediterranean Water. In fig. lb the thermoclines visible in XBT curves are indicated by dotted lines. Below, LITERATURE both the North Atlantic Currentnorth and south branch thermoclines are visible. In the BAKER, A. de C., M.R. CLARKE & M.J. HARRIS, 1973 The N.I.O. combination net (RMT1+8) North Atlantic Central Water surface layers and show the spring development of a thermocline further developments of rectangular midwater trawls. J. mar. biol. Ass. U.K., 53: south of 35 N, while south of 29 N a probably HEYMAN, R., in press. Narcotisation, fixation constant thermocline at 150 m depth is found below a newly developing one at ca 50 m depth. zoo and preservation experiments with marine plankton. Versl. techn. Geg. ITZ (AMNAPE, Proj. 101A, rep. no. 2). Test station 9 was made in water mass of 10 C, isothermal to a depth of 400 m, probably ROE, H.S.J., A. de C. BAKER, R.M. CARSON, R. the North Atlantic Current is found near this WILD & D.M. SHALE, Behaviour of the Institute of Océanographie Science's rectangular midwater trawls: Theoretical aspects and experimental observations. Mar. Biol., locality. The conditions of test station 27 in 56: Prof. Dr. S. van der Spoel, Instituut voor Taxonomische Zoologie, Plantage Middenlaan 53, 1018 DC Amsterdam, received : 13.XI The Netherlands. mailed :

Rl8 D the the the 9' 1 16.35 Rl8 8 Table I. Station list date day, month position geographic position at the beginning of each haul aver.

8 Rl8 D the the the 9' Rl8 8 Table I. Station list date day, month position geographic position at the beginning of each haul aver. crse the average course of the ship during the haul haul in min./km duration in minutes and the distance towed.in kilometres during the haul at surface: temp./sal. temperature (in 0 C) and the salinity (in "/ ) / OO' at the start of the haul at the sea surface temp. depth the average temperature (in C) over the depth sampled gear = Rectangular Midwater Trawl RMT1+8 R01 = Open Rectangular Midwater Trawl RMT1 ; RNR = Open Ringnet with RMT1 liner; RDD Open double Ringnet; RNO = Open Ringnet; 000 = collected by hand period = day; DN = dusk; N = night; ND = dawn st. haul date position aver depth haul in time at surface 1980 N: W: crse in m min. km start sal. temp. temp. depth gear period ' ' ' ' ' ' Rl8 D D RI8 D ' R01 D ' io ' ' Rl8 D ' ' RNO D ' ' R18 D ' ' R01 N il ' ' Rl8 D ' 29 5i 1' Rl8 D ' ' R18 D o Rl8 D ' ' RNO DN ' ' R01 DN 12 l ' ' ROl D ' ' RNO D o 545' ' ROl D 13 l I ' 30 0l.3' Rl8 N l.1' 30 oo.6' Rl8 N ' ' Rl8 N ' Rl8 N ' ' Rl8 ND ' 29 l8.5' Rl8 D ' ' R01 D 13 H ' ' RNO D ' ' RI8 D ' ' Rl8 D ' ' R18 D D ' ' RNO Rl8 DN i.8' ' Rl8 N ' R01 N ' Rl8 N ' ' RNO D ' ' R01 D l 56.4' ' Rl8 D i 5l.8' Rl8 D l 47.8' ' Rl8 D l 39.1' ' R18 D ' ' Rl8 D l 31.6' ' Rl8 DN l 35.9' ' RNO D ' ' RNO DN l 3l7' ' ROl DN l 0l.4' ' Rl8 N ' ' R18 N l l5.8' ' Rl8 ND ' ' Rl8 D ' ' ROl D ' D ' ' R18 N ' 36 l8.l R18 N ' 36 l8.7' RNO N ' 36 l Rl8 N ' 36 l6.2' RNR N continued overleaf

9 Table I (continued) st. haul date position aver. depth haul in time at surface temp. 1980 N: W: erse in m min. km start temp. sal. depth gear period 18 6 22.4 39 45.2' 36 13.1 1 65 50100 52 3.20 07.

9 9 Table I (continued) st. haul date position aver. depth haul in time at surface temp N: W: erse in m min. km start temp. sal. depth gear period ' R18 ND ' ' Rl8 D ' ' Rl8 D ' ' Rl8 D ' ' Rl8 D ' ' Rl8 D ' ' Rl8 N ' ' RNO N ' ' Rl8 D ' ' RNR D l ' ' Rl8 D ' ' RDD D Ô.l ' Rl8 D ' ' Rl8 D ' ' Rl8 D ' ' R18 D ' 3l 49.3' RNO D ' 3l 44.9' Rl8 D i8.i' 3l 36.7' Rl8 DN ' 3i 32.5' Rl8 N ll.o' 3i 29.2' Rl8 N ll3' 3l 29.3' RNO N ' 3l 3l.6' Rl8 N ' 3l 30.5' RNR N ' l ' Rl8 D ' ' Rl8 DN ' ' Rl8 N ' ' Rl8 N ' ' RNO N ' ' RNR N ' ' Rl8 N ' l Rl8 ND l ' Rl8 D ll.4' ' Rl8 D ll.9' ' RNR D ' ' RNR D ' ' R18 DN l ' ' Rl8 N l 58.2' ' Rl8 N ' RNO N l 559' ' R18 N ' ' Rl8 D ' ' R18 D ' ' RNR D ' I ' Rl8 N ' ' R18 N ' ' Rl8 ND ' RNO N ' ' R18 D l ' Rl8 D ' Rl8 DN ' ' Rl8 N i.0' ' RNR N ' R18 N ' ' ' 29 o 56.0' Rl8 N RNO N ' ' Rl8 N ' ' Rl8 ND ' ' RNO ND ' ' Rl8 D ' ' RNR D ' ' RNO D ' ' R18 D ' ' RNR D ' ' Rl8 D ' ' Rl8 DN ' ' RNO DN continued overleaf

10 10 Table I (continued) st. haul date position aver. depth haul in time at surface temp. gear period 1980 N: W: erse in m min. km start. temp. sal. depth ' ' Rl8 ND ' ' RNO ND ' ' Rl8 D ' ' RNR D ' ' Rl8 D ' 28 o 40.4' Rl8 D ' ' Rl8 D ' ' RNR D ' ' Rl8 DN ' ' RNO DN Table II: Secchi disc readings (white, Ф 91 cm) date time depth position in m N w 15IV ' 17IV ' ' 18IV ' IV ' ' 26IV ' ' 27IV ' ' 28IV ' ' 29IV ' ' v ' oo.4' 02 V ' l 1 1

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