We describe the design, manufacture, commissioning, and performance of PMAS, the Potsdam Multi-Aperture Spectrophotometer. PMAS is a dedicated integral field spectrophotometer, optimized to cover the optical wavelength regime of 0.35-1 µm. It is based on the lens array -fiber bundle principle of operation. The instrument employs an all-refractive fiber spectrograph, built with CaF 2 optics, to provide good transmission and high image quality over the entire nominal wavelength range. A set of user-selectable reflective gratings provides low to medium spectral resolution in first order of approx. 1.5, 3.2, and 7 Å, depending on the groove density (1200, 600, 300 gr/mm). While the standard integral field unit (IFU) uses a 16×16 element lens array, which provides seeing-limited sampling in a relatively small field-of-view (FOV) in one of three magnifications (8×8, 12×12, or 16×16 arcsec 2 , respectively), a recently retrofitted bare fiber bundle IFU (PPak) expands the FOV to a hexagonal area with a footprint of 65×74 arcsec 2 . Other special features include a cryogenic CCD camera for field acquisition and guiding, a nod-shuffle mode for beam switching and improved sky background subtraction, and a scanning Fabry-Pérot etalon in combination with the standard IFU (PYTHEAS mode). PMAS was initially designed and built as an experimental traveling instrument with optical interfaces to various telescopes (Calar Alto 3.5m, ESO-VLT, LBT). It is offered as a common user instrument at Calar Alto under contract with MPIA Heidelberg since 2002.

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The dominant sources of the petrogenic hydrocarbon background in benthic sediments of Prince William Sound, AK (PWS), site of the 1989 Exxon-Valdez oil spill, are eroding Tertiary shales and residues of natural oil seepage. Mass balance considerations and statistical analyses of hydrocarbon fingerprints independently indicate that coal contributes generally less than 1% of the polycyclic aromatic hydrocarbons (PAH) and chemical biomarkers in this background. This is environmentally significant because of presumed differences in the bioavailability of PAH in coal, seep oil residues, and shales. Coal particles are present in PWS sediments, but their PAH and chemical biomarker contributions are overwhelmed by those of seep oil residues and organic particles from shales of low-to-high thermally maturity. In the late Tertiary or early Quaternary, the currently exposed and eroding shale formations were heated into the oil-generation window and, consequently, are now relatively rich in extractable PAH and chemical biomarkers. The exposed and eroding coals in the area, in contrast, experienced long hot burial and are now thermally overmature with respect to oil generation. The concentrations of thermally sensitive PAH and biomarker compounds in PWS sediments are not consistent with a mature coal origin but are consistent with the low-to-high maturity shales and seep oils in the area.

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