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doi:10.2204/iodp.proc.329.102.2011

Physical properties

Physical property measurements provide fundamental information required to characterize lithostratigraphic units and allow for the correlation of cored materials with downhole logging data. The primary objective of the Expedition 329 physical properties program was to collect high-resolution data to document microbial habitats in both the sedimentary and basement environments. A variety of techniques and methods were used to characterize Expedition 329 sediment and basement core samples.

In general, three holes were drilled at each site after a pilot hole was washed in. Generally the first hole (Hole B) was dedicated to physical property measurements and the other two or more holes had whole rounds removed for geochemical or microbiological sampling. The remains of these cores were also logged and measured for physical properties but often at increased measurement spacing because of the now-incomplete sections.

Recovered whole-round cores were first allowed to thermally equilibrate to ambient room temperature of ~20°C (3 h for hard rock and 4 h for sedimentary material). After thermal equilibration, core sections with continuous intervals longer than 8 cm were run through the WRMSL for measurement of gamma ray attenuation (GRA) density, magnetic susceptibility, and compressional wave velocity (P-wave logger [PWL]). The noncontact resistance logger was not functional during Expedition 329. Sections longer than 50 cm were measured with the spectral Natural Gamma Ray Logger (NGRL).

After measurements with the WRMSL and NGRL, the cores were split into archive and working halves. The archive half of the core sections was passed first through the SHIL to quickly obtain a digital image of the core section and avoid color changes caused by sediment oxidation and drying (see “Lithostratigraphy, igneous petrology, alteration, and structural geology”). Subsequently, the archive half sections were run on the SHMSL for measurement of point magnetic susceptibility and spectrophotometry (sediment color reflectance, see below). The SHMSL also uses a laser to detect cracks and gaps along the core.

Thermal conductivity was measured using the Teka (Berlin, Germany) thermal conductivity instrument. For cores with unlithified sediment, thermal conductivity measurements were carried out on whole-round core sections using the needle probe technique. For lithified sediment or basement samples, thermal conductivity was measured on split core using the half-space technique. In all cases thermal conductivity was measured using the Teka thermal conductivity instrument.

Discrete samples were taken from the working half at intervals of ~1 or 2 per core. Discrete measurements were used to measure compressional wave velocity in three directions, and moisture and density (MAD) samples were taken to measure wet bulk density, dry bulk density, grain density, water content, void ratio, and porosity. A comprehensive discussion of methodologies and calculations used in the JOIDES Resolution Physical Properties Laboratory is presented in Blum (1997). Details about each physical property measurement are described below.

Whole-Round Multisensor Logger measurements

GRA bulk density and magnetic susceptibility were measured nondestructively with the WRMSL. To optimize WRMSL performance, sampling intervals and measurement integration times were the same for all sensors. Sampling intervals were set at 2 cm with an integration time of 5 s for each measurement. These sampling intervals are common denominators of the distances between the sensors installed on the WRMSL (30–50 cm) and allow sequential and simultaneous measurements. GRA performance was monitored by passing a single core liner filled with deionized water through the WRSML after every core.

In general, measurements are most effective on materials that completely fill the core liner and have minimal drilling disturbance. For sediment cores, the core liner has a diameter of 66 mm and is assumed to be filled. Basement sections are cored with a maximum diameter of 58.5 mm, and recovered pieces are often smaller than the maximum diameter. Therefore, GRA bulk density and magnetic susceptibility measurements tend to underestimate true values. This bias is minimized by multiplying basalt densities by 66/58.5 = 1.18. Additionally, many measurements of density suffer from dropouts caused by gaps between core pieces. Dropouts were minimized by removing densities <2 g/cm³.

Gamma ray attenuation bulk density

The GRA densiometer on the WRMSL operates by passing gamma rays from a ¹³⁷Cs source through a whole-round core into a 75 mm × 75 mm sodium iodide detector situated directly below the core. The gamma ray peak has a principal energy of 0.662 MeV and is attenuated as it passes through the core (Evans, 1965; Harms and Choquette, 1965). The attenuation of gamma rays, mainly by Compton scattering, is related to the material bulk density and thickness of sample. The gamma ray count is proportional to density. Bulk density, ρ, determined with this method can be expressed as

where

• µ = Compton attenuation coefficient,
• d = sample diameter,
• I₀ = gamma ray source intensity, and
• I = measured intensity of gamma rays passing through the sample.

The values µ and I₀ are treated as constants, such that ρ can be calculated from I. The gamma ray detector is calibrated with a set of aligned aluminum cylinders of various diameters surrounded by distilled water in a sealed core liner that is the same as that used during coring operations. The relationship between I and the product of µ and d can be expressed as

where A, B, and C are coefficients determined during calibration. Gamma ray counts through each cylinder were determined for a period of 60 s, and the natural log of resulting intensities was plotted as a function of µd. Here, ρ of each aluminum cylinder was 2.7 g/cm³, and d was 1, 2, 3, 4, 5, or 6 cm. These coefficients fluctuated slightly during the time period over which the measurements were made, as indicated by repeated calibrations. The WRMSL provided the values of I and µ, and ρ was calculated with the above equation. Recalibration was performed as needed if the deionized standard after every core deviated significantly (more than a few percent) from 1 g/cm³. The spatial resolution of the GRA is <1 cm.

Magnetic susceptibility

Magnetic susceptibility, k, is a dimensionless measure of the degree to which a material can be magnetized by an external magnetic field,

where M is the magnetization induced in the material by an external field strength H. Magnetic susceptibility responds to variations in the magnetic composition of the sediment that commonly can be related to mineralogical composition (e.g., terrigenous versus biogenic materials) and diagenetic overprinting. Materials such as clay, possibly from alteration of igneous materials, have a magnetic susceptibility several orders of magnitude lower than magnetite and some other iron oxides that are common constituents of igneous material. Water and plastics (core liner) have a slightly negative magnetic susceptibility.

The WRMSL incorporates a Bartington Instruments MS2 meter coupled to a MS2C sensor coil with a diameter of 8.8 cm operating at a frequency of 565 Hz. The sensor output can be set to centimeter-gram-second (cgs) units or SI units, with the IODP standard being the SI setting. The core diameter is smaller than the aperture through which it passes to be measured. Therefore, a volume correction factor must be applied to the data offline. Assuming a core diameter of 66 mm and using the coil aperture of 88 mm, the correction factor simply entailed multiplying the 10^–5 SI units by a factor of 0.68 (Blum, 1997).

The instrument is calibrated with a homogeneous mixture of magnetite and epoxy in a 40 cm long piece of core liner to an accuracy of ±5%. However, this calibration is a factory preset. The resolution of the method is ±4 cm; therefore, core material that is not continuous over an 8 cm interval underestimates the magnetic susceptibility.

P-wave logger measurements

P-wave velocity varies with lithology, porosity, and bulk density of material; state of stress; temperature; and fabric or degree of fracturing. In sediment and rock, velocity is controlled by degree of consolidation and lithification. Because the contact between the core liners and hard rock samples is often poor, P-wave velocity measurement was not run on basement cores.

The PWL sensor measures the ultrasonic P-wave velocity of the whole-round sample residing in the core liner. The PWL transmits a 500 kHz P-wave pulse across the core section at a specified repetition rate. This signal is coupled to the sample by the plastic pole contacts of the transducers clamped to the sides of the core by the linear actuator. No water is used to improve coupling between the transducers and the liner. The plastic pole contacts and the pressure applied by the actuator are sufficient for reliable P-wave measurement. The transmitting and receiving ultrasonic transducers are aligned so that wave propagation is perpendicular to the long axis of the core section. Torque applied by the actuator can be set by the user to ensure good acoustic contact between the liner and the core material.

The basic relationship for sonic velocity, V, is

where d is the path length of the wave through the core and t is the traveltime. The total traveltime between the transducers includes three components:

• t_delay (time delay related to transducer faces and electronic circuitry),

• t_pulse (delay related to the peak detection procedure), and

• t_liner (transit time through the core liner).

The system is calibrated using a core liner filled with pure water. For routine measurement on whole-round cores inside core liners, the corrected core velocity, V_core, can be expressed by

where

• d′_core = measured diameter of core and liner,
• d_liner = liner wall thickness, and
• t₀ = measured total traveltime.

Traveltime is determined by signal-processing software that automatically detects first arrival of the P-wave signal to a precision of 50 ns. It is a challenge for an automated routine to pick the first arrival of a potentially weak signal if background noise is high. The search method skips the first positive amplitude and finds the second positive amplitude using a detection threshold limit, typically set to 30% of the maximum amplitude of the signal. It then finds the preceding zero crossing and subtracts one wave period to determine the first arrival. To avoid extremely weak signals, minimum signal strength can be set (typically 0.02 V) and weaker signals are ignored. To avoid signal interference at the beginning of the record from the receiver, a delay (typically 0.01 ms) can be set to force the amplitude search to begin in the quiet interval preceding the first arrival. In addition, a trigger (typically 4 V) is selected to initiate the arrival search process, and the number of waveforms to be stacked (typically five) can also be set. A linear voltage differential transformer measures the separation of the transducer to derive a signal path length (i.e., the core diameter). After corrections for system propagation delay, liner thickness, and liner material velocity, the ultrasonic P-wave velocity is calculated.

Natural Gamma Radiation Logger measurements

The NGRL installed on the JOIDES Resolution was designed and built at the Texas A&M University (College Station, Texas, USA) IODP facility between 2006 and 2008. The NGRL measures gamma rays emitted from whole-round core sections arising primarily from the decay of ²³⁸U, ²³²Th, and ⁴⁰K isotopes.

The main NGR detector unit consists of 8 sodium iodide (NaI) scintillator detectors, 7 plastic scintillator detectors, 22 photomultipliers, and passive lead shielding. The NaI detectors are covered by 8 cm of lead shielding. In addition, lead separators (~7 cm of low-background lead) are positioned between the NaI detectors. Half of the lead shielding closest to the NaI detectors is composed of low-background lead, whereas the outer half is composed of regular (virgin) lead. In addition to passive lead shielding, the NGRL employs a plastic scintillator to suppress the high-energy gamma and muon components of cosmic radiation by producing a cancelling signal when these charged particles pass through the plastic scintillators. The NGRL was calibrated using a source consisting of ¹³⁷Cs and ⁶⁰Co and identifying the peaks at 662 and 1330 keV, respectively. Calibration materials are provided by Eckert and Ziegler Isotope Products, Valencia, California (USA).

For presentation purposes, the counts were summed over 100–3000 keV and are thus comparable with data collection from previous cruises and are appropriate for direct comparison with downhole logging data. Background measurements of an empty core liner counted for 20,000 s (5 h) were made upon arrival at each site. Over the 100–3000 keV integration range background counts averaged 4–5 cps and contributed <0.5% to the overall signal of the measured core.

A measurement run consisted of eight measurements offset by 20 cm each, first at one position and measured at a second position shifted 10 cm from the first (for a total of 16 measurements, each 10 cm apart, for a 150 cm long section of core). The quality of the energy spectrum measured in a core depends on the concentration of radionuclides in the sample, but also on the counting time, with higher times yielding better spectra. The available count time in each position depends on core flow through the lab.

In general, we had the opportunity to count for longer times, yielding statistically significant energy spectra. Count times ranged between 1800 and 5400 s for each position, resulting in total count times of 1–3 h per section. Shorter count times were used on holes where whole rounds had been sampled for geochemistry or microbiology. These times were ~1800 s or less. Improved spectral resolution allows qualitative identification of the main contributors to the energy spectra (i.e., products of the ⁴⁰K, ²³²Th, or ²³⁸U decay chains). Building a database of well-resolved spectra works toward the goal of separating ⁴⁰K, ²³²Th, and ²³⁸U contributions and eventual quantifying concentrations of the radionuclide daughters.

Section Half Multisensor Logger measurements

The SHMSL measures magnetic susceptibility and spectral reflectance on core-section halves. The archive half of the split core is placed on the system’s core track. An electronic platform moves along a track above the core section, recording the sample height with a laser sensor. The laser establishes the location of the bottom of the section and the platform reverses the direction of movement, moving from bottom to top making measurements of point magnetic susceptibility and spectral reflectance data at 2 cm intervals.

Color reflectance spectrometry

Reflectance is measured from 171 to 1100 nm wavelength at 2 nm intervals using a halogen light source, covering wavelengths from ultraviolet through visible to near infrared. The scan of the entire wavelength range takes ~5 s per data acquisition offset. The data are generated using the L*a*b color system, in which L* is luminescence, a* is the blue + green values, and b* is the red + green values. The color reflectance spectrometer calibrates on two spectra: pure white (reference) and pure black (dark). Color calibration was conducted approximately every 12 h.

Point magnetic susceptibility

Point magnetic susceptibility is measured using a contact probe with a flat 15 mm diameter sensor operating at a frequency of 0.580 kHz. The sensor averages three measurements at 0.1 attenuation for each offset to an accuracy of 5%. The spatial resolution of the magnetic susceptibility point instrument is 20 mm, making it advantageous over whole-round magnetic susceptibility for basement cores consisting of broken pieces smaller than 8 cm (the spatial resolution of whole-round magnetic susceptibility). Units are reported in dimensionless SI units on a volume basis. The point magnetic susceptibility meter was calibrated by the manufacturer before its installation on the ship. The probe is zeroed in air before each measurement point, and a background magnetic field (i.e., influence from metal track and so on) is measured and removed from the data before being output. The instrument calibration assumes that the probe is buried in the sample. However, because the probe is only in contact with the upper, flat surface, a correction factor of 2× was applied after the data were collected. Note that the data stored in LIMS have not had this correction applied.

Thermal conductivity

Thermal conductivity is the rate at which heat flows through a material and is dependent on composition, porosity, and structure. Thermal conductivity was measured on unconsolidated sediment and rock samples using either the full-space needle probe (Von Herzen and Maxwell, 1959) or the half-space line source (Vacquier, 1985), respectively. Both the full- and half-space methods approximate the heating element as an infinite line source (Blum, 1997). These measurements produce a scalar value in a plane perpendicular to the orientation of the probe. All measurements were made after the cores had equilibrated to ambient laboratory temperature. At the beginning of each measurement, temperatures in the samples were monitored to ensure that the background thermal drift was <0.04°C/min. After the background thermal drift was determined to be stable, the heater circuit was closed and the increase in the probe temperature was recorded. In most cases, the reported thermal conductivity value for full-space needle-probe measurements is the average of at least three repeated measurements. Reported half-space line-source thermal conductivity values typically represent the average of between five and ten repeated measurements. Based on these repeated measurements, individual measurements are usually within 1% of the mean for both full- and half-space measurements. Both of these values are within the stated uncertainty of 5% (Blum, 1997). All data are corrected to in situ pressure and temperature, assuming a hydrostatic pressure gradient and a background temperature gradient based on advanced piston corer temperature tool (APCT-3) measurement. The pressure correction is +1% for each 1800 m depth (Ratcliffe, 1960).

In porous rock, temperature influences thermal conductivity in two competing ways. The thermal conductivity of rock matrix is inversely related to temperature (Zoth and Haenel, 1988), whereas the thermal conductivity of water increases with temperature (Keenan et al., 1978). The temperature correction is +1% for each +20°C change in temperature between the laboratory and in situ conditions, a value intermediate between the +5% suggested by Ratcliff (1960) for a high-porosity, water-saturated sediment and the mean value of –3% derived from data reported by Clark (1966) for several hard rocks. Both uncorrected and corrected values of thermal conductivity are reported.

Soft-sediment full-space measurements

A full-space, single-needle TeKa TK04 probe unit (Blum, 1997) was utilized to measure thermal conductivity of whole cores. To insert this probe, a 2 mm hole was made in the core liner at a position based on visual inspection of the core. Needle probes consist of a heater wire and a thermistor. At the beginning of each measurement, temperature in the sediment is monitored to ensure that a thermal drift of no more than 0.4 mK/min is present. This step normally takes a minute or two. After the temperature field is determined to be near equilibrium, a calibrated heat source is applied and the rise in temperature is recorded for ~80 s. Values of thermal conductivity are based on the observed rise in temperature for a given quantity of heat. In most cases, repeated measurements were made at the same location. For these repeated measurements, the needle probe is left in place and the sample is left to reequilibrate for 10 min prior to the next measurement. Consequently, most of the time a measurement takes is waiting for the sample to reequilibrate.

Lithified sediment and hard rock half-space measurements

Thermal conductivity on basement samples was measured on the archive half of the split core with the thermal conductivity meter in half-space mode (Vacquier, 1985). Samples must be smooth to ensure adequate contact with the heating needle. Visible saw marks were removed when necessary by grinding and polishing the split surface with 120–320 gauge silicon carbide powder. Most samples did not require polishing. Basement samples equilibrated to room temperature in a seawater vacuum saturator for 24 h, and sample and sensor needle were equilibrated together in a cooler insulated with styrofoam for at least 15 min prior to measurement. Isolation of the sample and sensor needle eliminated the effect of rapid but small temperature changes introduced by air currents in the laboratory. The instrument internally measures drift and does not begin a heating run until sufficient thermal equilibrium is attained. Cores were measured at irregular intervals (aiming for one sample per section) depending on the availability of homogeneous and relatively vein/crack-free pieces long enough to be measured without edge effects (pieces at least 7 cm long; i.e., longer than the instrument needle).

Formation factor

Formation factor was determined from electrical conductivity measurements taken every 10 cm on split sediment cores. Formation factor may be used to quantify chemical fluxes through the sediment. For these measurements, two in-line electrodes, 1.5 cm long and spaced 1 cm apart in a block of nonconducting flouoropolymer and attached to a Metrohm 712 conductometer, were inserted into the split-core sediment. Standards were measured before and after approximately every seventh measurement. This means that a standard was measure prior to, in the middle of, and after each core section.

At each sampling location, measurements of sediment conductivity, χ_sed (the inverse of resistivity, R_core), and sediment temperature were made. Measurement of seawater conductivity, χ_sw, and its temperature were made regularly.

Both seawater and sediment measurements of electrical conductivity were adjusted to a standard temperature of 20°C where the correction factor is given by a fifth-order polynomial (Janz and Singer, 1975),

where

• a = 29.05128,
• b = 0.88082,
• c = –0.000198312,
• d = 0.00033363,
• e = –0.000010776, and
• f = 0.000000112518.

The temperature corrected measurement, σ_T, is given by

where σ is the measurement and χ₂₀ and χ_obs are the correction factors using 20°C and the observed temperature, respectively. Both seawater and sediment measurements of electrical conductivity are adjusted for the effects of temperature. A linear drift correction based on the seawater measurements is computed and applied to both the sediment and seawater temperature adjusted measurements and the formation factor, F, is computed as,

This simple method for determining formation factor does not take into account surface conductivity effects of the sediment matrix. However, this is not of concern in high-porosity sediments where the conductive pathways depend dominantly on intergranular porosity and pore connectivity, even where the sediment matrix contains significant clay.

Discrete sample measurements

Cubic samples were cut from the working halves of split cores at an interval of ~1 sample per section for both sediment and basement cores. These ~7 cm³ samples aimed to best represent the general variation and lithologies of the core. The purpose of these samples is two-fold. First, they are used for physical property measurements of compressional wave velocity and moisture and density measurements (discussed below). Second, discrete samples were shared with paleomagnetists to minimize core depletion.

Moisture and density

Several basic quantities of interest (water content, bulk density, dry density, porosity, and void ratio) are found most accurately through mass and volume determinations on discrete samples. MAD data are also used for comparison with GRA bulk density data from the WRMSL. The shipboard MAD facility on the JOIDES Resolution includes a dual-balance system and a hexapycnometer. During Expedition 329, only five cells were available, transforming this system to a pentapycnometer. For hard rock samples, a vacuum water saturator is also used.

Vacuum water saturator

Basement samples were saturated in a vacuum-pump system. Samples were placed in a plastic chamber filled with seawater. A vacuum pump removed the air from the chamber, drawing seawater into the samples. The samples were saturated for at least 24 h. During this time, the vacuum was checked at 2–3 h intervals for possible leaks. After removal from the saturator, the cubes were stored in sample containers filled with seawater to help prevent evaporation of interstitial water. Next, the cube surfaces were patted dry with a paper towel and wet mass was immediately determined using the dual-balance system.

Dual-balance system

The dual-balance system was used to measure both wet and dry masses. The two analytical balances (Mettler-Toledo XS204) were used to compensate for ship motion, one acting as a reference and the other for measurement of the unknown. A standard weight of similar value to the sample was placed on the reference balance to increase accuracy. The default setting of the balances is 300 measurements (taking ~1.5 min).

Hexapycnometer system

The hexapycnometer system measures dry sample volume using pressurized, helium-filled chambers. At the start of the expedition and whenever the helium gas tank was changed, shipboard technicians performed a calibration using stainless steel spheres of known volume. A batch of samples consisted of four cells with samples of unknown volumes and one cell with two stainless steel spheres (3 and 7 cm³). The spheres were cycled through the cells to identify any systematic error and/or instrument drift. Spheres are assumed to be within 1% of their total volume. Individual volume measurements were preceded by three purges of the sample chambers with research-grade (99.995% or better) helium heated to 28°C, followed by three data acquisition cycles.

Wet and dry mass measurements

Immediately after sediment samples were collected or basement samples were saturated, the wet sediment mass (M_wet) was measured. Dry sediment mass (M_dry) and volume (V_dry) were measured after drying the samples in a convection oven for >24 h at a temperature of 105° ± 5°C. Dried samples were then cooled in a desiccator for >1 h before the dry mass was measured. Dry volume was measured using a helium-displacement pycnometer with a nominal precision of ±0.04 cm³. Each reported value consists of an average of three measurements. A reference volume (calibrated sphere) was run with each group of four samples, and the sphere was rotated between cells to check for systematic error.

For calculation of sediment bulk density, dry density, grain density, porosity, and void ratio, the traditional ODP method was used (Method C). Water content, porosity, and void ratio were defined by the mass or volume of extracted water before and after removal of interstitial water through the drying process. Standard seawater density (1.024 g/cm³) was used for the density of interstitial water. For basement samples that were too vesicular to saturate, we calculated these values using “Method D,” where volume is determined by caliper rather than by saturation and helium-displacement pycnometer.

Water content

Water content (W_c) was determined using the methods of the American Society for Testing and Materials (ASTM) designation D2216 (ASTM International, 1990). Corrections are required for salt when measuring the water content of marine samples. In addition to the recommended water content calculation in ASTM D2216 (i.e., the ratio of pore-fluid mass to dry sediment mass [percent dry weight]), we also calculated the ratio of pore-fluid mass to total sample mass (percent wet weight). The equations for water content were

and

where

• M_t = total mass of the saturated sample,
• M_d = mass of the dried sample, and
• r = salinity.

Bulk density

Bulk density (ρ) is the density of the saturated samples, with ρ = M_t/V_t. The mass, M_t, was measured using the balance, and V_t was determined from the pycnometer measurements of grain volume and the calculated volume of the pore fluid (V_t = V_pore + V_d). For the high-porosity samples from Expedition 329, bulk density was determined directly from ρ = M_t/V_t.

Porosity

Porosity (φ) was calculated using

where

• ρ = measured bulk density,
• ρ_w = density of the pore fluid, and
• W_c = water content expressed as a decimal ratio of percent dry weight.

Grain density

The grain density (ρ_grain) was determined from measurements of dry mass and dry volume made in the balance and in the pycnometer, respectively. Mass and volume were corrected for salt using

where s is the salt content (in grams) and ρ_salt is the density of salt (2.257 g/cm³).

Compressional wave velocity

Discrete compressional wave (P-wave) velocity measurements were obtained on sediment cores at a frequency of one per core. For basement samples, we used the same discrete cube samples that were also used for MAD and paleomagnetism determinations. P-wave measurements were performed on seawater-saturated samples directly after wet mass determinations were made. Measurements used the x-axis caliper-type contact probe transducers on the P-wave velocity gantry. Oriented samples were rotated manually to measure y- and z- axis velocities with the same instrument. The system uses Panametrics-NDT Microscan delay line transducers, which transmit at 0.5 MHz. To maximize contact with the transducers, deionized water was applied to sample surfaces.

The signal received through the sample was recorded by the computer attached to the system, and the peak of the initial arrival was chosen with autopicking software. The complete waveform was stored with the data in case reanalysis is deemed necessary. However, visual checks of the picks made on board appeared satisfactory. The distance between transducers was measured with a built-in linear voltage displacement transformer (LDVT).

Calibration was performed each day, before measurements were made, with a series of acrylic cylinders of differing thicknesses and known P-wave velocity of 2750 ± 20 m/s. The determined system time delay from calibration was subtracted from the picked arrival time to yield a traveltime of the P-wave through the sample. The thickness of the sample (calculated by LDVT in meters) was divided by the traveltime (in seconds) to calculate a P-wave velocity in meters per second.

Downhole temperature measurements

Downhole temperature measurements were made using the APCT-3. The APCT-3 is the third-generation tool of its kind and is used with advanced piston coring. The APCT-3 consists of three components: electronics, coring hardware, and computer software (Heeseman et al., 2006). In this expedition, downhole temperature measurements were made approximately every third core during APC coring when sediments were thick enough. The temperature sensors were calibrated for a working range of 0°–45°C.

Before entering a hole, each instrument was held at the mudline for ~5 min to equilibrate with bottom water temperature. After bottom water temperature equilibration, the tools were lowered down the hole and penetrated the formation. The penetration of the tool into the formation caused a rise in temperature because of frictional heating. Following the initial temperature rise, temperatures decreased along a decay curve to near equilibrium. During this decay phase, it is important that the temperature tool is not disturbed. A second rise in temperature was due to frictional heating as the tool was pulled out of the formation. Temperatures were measured as a time series with a sampling rate of 1 s and logged onto a microprocessor within the downhole tool. Data were retrieved when the tool was recovered. The formation equilibrium temperature was determined based on fitting the temperature decay curve using the program TP-Fit, which runs on MATLAB (M. Heeseman et al., pers. comm., 2008).

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