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A multicalorimeter is described which allows the measurement of heat production of up to 10 sediment samples simultaneously. System regulation a s well as data processing and evaluation are performed by personal computer. The instrument performs well even a t non-controlled room temperature down to -0.5"C on board a research vessel. First results from tests employing pressure chambers are presented. An example for a deep-sea heat-production proflle 1s given from the Norwegian Basin, depichng subsurface maxlma in benthic activity. Direct microcalorimetry has been widely used in biological sciences (Wadso 1975, Ljungholm et al. 1980, Gnaiger 1983, Lock & Ford 1985). In biological oceanography the technique has been used for the investigation of anaerobic metabolism of benthic invertebrates (Pamatmat 1978, Famme & Knudsen 1983, Shick 1981, Hammen 1983) and of soft bottom community metabolism (Pamatmat 1982). The method measures simultaneously all types of metabolism in a community; thus the rate of heat loss is enthalpy change and the last step of energy flow through the system. The combustion value of metabolized organic matter is equivalent to the released heat. The method has been used to calculate carbon budgets (Graf et al. 1982, 1983). Recently, the reliability of these budgets was demonstrated by direct calorimetry of a predominantly anaerobic sediment (Graf 1987). By comparison, oxygen consumption, also called indirect calorimetry, only accounted for the topmost few milhmeters of sediment activity and greatly underestimated the amount of metabolized organic matter in the lower layers. Most calorimeters used are of the heat conduction type. These work isothermically and need long equilibration times (Calvet 1956), making direct calorimetry Q Inter-Research/Pnnted In F. R. Germanv a relatively slow method. To overcome this problem, it is desirable to increase the number of devices in use simultaneously. An example is given by the Pamatmat double twin calorimeter (Pamatmat 1978). In the present article we present a multicalorimeter which can measure 10 samples simultaneously, thus enabling the measurement of a sediment heat flow profile in one run. Other features of the instrument for calorimetry of sediments have been improved. The multicalorimeter works at low temperature on board shlp and accomodates larger samples than commercially available instruments. Furthermore the chambers can be compressed to simulate in situ pressure up to 310 bar. Description of the instrument. The calorimeter block is placed inside a PVC-covered aluminium container (90 cm diameter) and fixed inside a well-insulated constant-temperature bath (Fig. 1). The aluminium container is completely submersed exept for PVC shafts through which samples are inserted into the instrument. Temperature is regulated by an external cooler (Braun, Frigomix 1497 and Thermomix 1480E), which is connected to a copper coil surroundng the container, and an internal heater (Braun Thermomix, 1480E), creating a accuracy of & 0.005 Co. A mixer increases turbulence in the water bath. It is possible to run the instrument at -0.5 "C at unregulated ambient room temperature. The calorimeter block is constructed from about 200 kg of aluminium and has the shape of a 10-armed star (Fig. 2). Fig. 3 shows 2 sections of this construction. The left side depicts a tangential section through 2 arms including the PVC shaft for sample insertion and removal (8). The left arm holds a V4A-steel chamber (6 cm external diameter) containing the sediment sam202 Mar. Ecol. Prog. Ser. 45: 201-204. 1988 Fig. 1. Temperature-regulating scheme of the m~~lticalorimeter External cooler (1) and internal heater (2) keep the calorimeter at constant temperature. Samples are introduced via the shafts (10) '0 2

A multicalorimeter for the study of biological activity in marine sediments