We developed preliminary age-depth models for all sites to calculate mass accumulation rates and to aid investigators with sediment sampling strategies. The age-depth control points were extracted from the composite sections for each site; thus, all sedimentation rates are reported in mcd/m.y.
Age-depth models were developed using both biostratigraphic and paleomagnetic control points as presented in "Biostratigraphy" and "Paleomagnetism". Typically, preference was given first to paleomagnetic data because of their higher sampling resolution, then to nannofossils (over foraminifers) because of generally better stratigraphic resolution. A Stineman function was fit to all data points for a local smoothing effect (geometric weight on current point and 10% of data range). This smoothed curve usually presented a reasonable average when different age datums from the same core-catcher sample were obtained. If the smoothed curve showed abrupt changes in slope as a result of the sampling error (sampling was usually every 10 m), apparent outliers were excluded from the model after discussion with the Leg 184 stratigraphers.
The smoothed age-depth curve was sampled every 5 m to provide the final model for each site. For each depth point x (m), linear sedimentation rates (LSR) were computed for the 10-m window defined by the adjacent depth points:
LSR = [depth(x - 5) - depth(x + 5)]/[age(x - 5) - age(x + 5)] [m/m.y.].For the calculation of mass accumulation rates (MAR), dry density data (DD = dry mass/wet volume [in grams per cubic centimeter]) and percent carbonate data (%CARB) were linearly interpolated every 5 m. Total mass accumulation was then computed as
MAR(total) = DD × LSR/10 [g/cm2/k.y.],and carbonate accumulation rate as
MAR(carbonate) = %CARB/100 × MAR(total) [g/cm2/k.y.].The long-term trends in LSR and MAR are not likely to change significantly based on future work. However, LSR and MAR may change considerably (orders of magnitude) over short intervals (e.g., orbitally controlled glacial or monsoonal cycles) that are not resolved with shipboard sampling and analysis. Also, despite the use of a smoothed age-depth model, the preliminary nature and coarse sampling rate may cause apparent changes in rates that should not be overinterpreted.