Kristina L Faul

Selective phosphorus regeneration of sinking marine particles: evidence from 31P-NMR

Phosphorus (P) regeneration and transformation in the oceanic water column and in marine sediments depends on the chemical nature of the sinking particulate P pool. For the first time, we have characterized the molecular composition of this pool, in various oceanic settings and water depths, using 31 P nuclear magnetic resonance (NMR) spectroscopy. Both inorganic P (orthophosphate, pyrophosphate, and polyphosphate) and organic P compounds (orthophosphate monoesters, orthophosphate diesters, and phosphonates) were identified. The inorganic P is present predominantly as orthophosphate with small amounts (<10%) of pyro- and polyphosphates. These inorganic compounds may be at least partially of biological origin. The relatively high abundance of inorganic P suggests that considerable transformation from the organic to the inorganic pool occurs in the water column. Some of this inorganic P may be present in association with mineral phases (apatite, clays, and oxyhydroxides) and thus may not be bioavailable. The distribution of organic P compounds in the sinking particulate matter pool is generally similar in composition to phytoplankton and significantly different than in the dissolved organic matter (DOM) pool. Results indicate that in most oceanic regions the majority of P regeneration occurs at very shallow depths. However, in the Ross Sea, a significant fraction of organic P is exported to depth below the euphotic zone. Hydrolysis of P compounds continues throughout the water column as indicated by a decrease in total particulate P with depth and a relative decrease in the organic P fraction at some sites. Orthophosphate monoesters dominate the organic P pool at all locations, followed by orthophosphate diesters. Phosphonates are present in a few samples but never contribute more than 6% of total extractable P compared to 25% abundance in the dissolved organic P (DOP) pool. This work shows that considerable spatial and temporal variability in the molecular composition of sinking particulate P exists. A more systematic study is needed to assess the different environmental parameters that affect the composition of particulate P and result in this variability. D 2003 Elsevier Science B.V. All rights reserved.

Application of sulphur isotopes for stratigraphic correlation

The sulphur isotopic composition of dissolved sulphate in seawater has varied considerably through time. Certain time intervals are characterised by distinct variations and a relatively high rate of change. These relatively rapid fluctuations allow for correlation of sediment sections using sulphur isotopes. Sulphur isotope reconstructions based on the analysis of carbonate associated sulphate or marine barite result in sulphur isotope records with an age resolution of 1–5 million years (Ma), and for some age intervals the resolution is<0.25 Ma. At these specific time intervals, where higher resolution records exist and excursions in the record are identified, the trends could be used for stratigraphic correlations. Such records are particularly useful in sections from deep marine sites that lack biostratigraphic controls or where biozones do not provide sufficient resolution.

Nutrient and paleoproductivity dynamics in the early Paleogene

For sustained warm climates like the early Paleogene, it is not well known how large amplitude, long-term changes in carbon cycling are related to nutrient burial and oceanic primary productivity. The Paleocene carbon isotope maximum (δC values as high as 4‰ centered around c. 57 Ma, for 2–4 m.y.) has been interpreted as a time of increased primary productivity and organic carbon burial (e.g., Shackleton 1985, 1987; Corfield & Cartlidge 1992; Corfield 1994; Schmitz et al. 1997; Thompson & Schmitz 1997). This large and global perturbation to the carbon cycle should be detectable in nutrient and productivity tracers in the sedimentary record. During the Paleocene δC maximum, global oceanic primary productivity may have been twice as high as today’s (Thompson & Schmitz 1997). Additionally, organic carbon burial may have been twice as high as today’s based on the δC of bulk calcite (Shackleton 1987) and possibly even higher if assumptions about total carbon input are changed (Delaney & Boyle 1988). Coupled records of tracers of nutrient burial and productivity will allow us to test these interpretations. Phosphorus (P) burial gives us insight into carbon cycling because P is the ultimate limiting nutrient in the oceans on long time scales (e.g., Tyrrell 1999). In modern open ocean settings such as the equatorial Pacific and the western Atlantic, barium (Ba) flux correlates well with export production (i.e., organic carbon flux from surface waters; e.g., Dehairs et al. 1980; Dymond et al. 1992; Paytan et al. 1996; Dymond & Collier 1996). We use sediment records of P burial to investigate nutrient burial in the Paleogene, and records of Ba burial to investigate paleoproductivity. We determined total reactive P (P that was originally biologically available in the water column) concentrations, calcium carbonate (CaCO3) contents, and effective organic carbon (C) concentrations spanning a time interval of c. 35–70 m.y. in a composite of sites from Blake Nose, Ocean Drilling Program (ODP) Leg 171B (Table 1). We also measured the carbon isotopic composition of bulk calcite at Site 1050. Effective organic C concentrations were defined by combustion oxygen demand, or COD, a method that measures the amount of reduced materials (primarily organic C) oxidized under combustion (Perks & Keeling 1998). To calculate total reactive P mass accumulation rates (MARs), we used the P concentrations with shipboard dry bulk densities and sedimentation rates defined by magnetostratigraphy for Site 1050 and Site 1051 and magnetostratigraphy supplemented by nannofossil stratigraphy for Site 1052. This is the first study of nutrient burial and paleoproductivity to apply a multiproxy accumulation rate approach to GFF volume 122 (2000), pp. 46–47. “Early Paleogene Warm Climates and Biosphere Dynamics”