Organic carbon production, mineralization and preservation on the Peruvian margin

Abstract

Abstract. Carbon cycling in Peruvian margin sediments (11° S and 12° S) was examined at 16 stations from 74 m on the inner shelf down to 1024 m water depth by means of in situ flux measurements, sedimentary geochemistry and modeling. Bottom water oxygen was below detection limit down to ca. 400 m and increased to 53 μM at the deepest station. Sediment accumulation rates and benthic dissolved inorganic carbon fluxes decreased rapidly with water depth. Particulate organic carbon (POC) content was lowest on the inner shelf and at the deep oxygenated stations (< 5%) and highest between 200 and 400 m in the oxygen minimum zone (OMZ, 15–20%). The organic carbon burial efficiency (CBE) was unexpectedly low on the inner shelf (< 20%) when compared to a global database, for reasons which may be linked to the frequent ventilation of the shelf by oceanographic anomalies. CBE at the deeper oxygenated sites was much higher than expected (max. 81%). Elsewhere, CBEs were mostly above the range expected for sediments underlying normal oxic bottom waters, with an average of 51 and 58% for the 11° S and 12° S transects, respectively. Organic carbon rain rates calculated from the benthic fluxes alluded to a very efficient mineralization of organic matter in the water column, with a Martin curve exponent typical of normal oxic waters (0.88 ± 0.09). Yet, mean POC burial rates were 2–5 times higher than the global average for continental margins. The observations at the Peruvian margin suggest that a lack of oxygen does not affect the degradation of organic matter in the water column but promotes the preservation of organic matter in marine sediments.

A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

“…Around 0.5 g of the freeze‐dried and homogenized sediment from the short cores MUC2 (outside the chimney) and MUC3 (inside the chimney) was analyzed to determine 210 Pb activity via its granddaughter isotope 210 Po using alpha‐spectrometry with a Canberra Passivated Implanted Planar Silicon detector. The average sedimentation rate was determined by simulating the measured excess 210 Pb activity data using a steady‐state diagenetic model that includes terms for sediment burial, bioturbation, compaction, and radioactive decay [ Dale et al ., ]. Identical 210 Pb‐derived sedimentation rates of 0.03 cm yr −1 were derived from both multicores and were applied to all GCs assuming that the sedimentation regime has not changed over, at least, the past few thousand years.…”

Records of past mid-depth ventilation: Cretaceous ocean anoxic event 2 vs. Recent oxygen minimum zones

“…This value is in good agreement with today's productivity of the Peruvian upwelling, and it is derived from a core interval, where an unusually thick section of laminations was preserved. Nonetheless, the Recent carbon burial efficiency at 10 cm sediment depth close to the SO147-106KL coring site amounts to 62 % of the organic matter arriving at the sea floor (Dale et al, 2014). It is thus much higher than burial rate estimates for the late Holocene (Müller and Suess, 1979).…”

“…Furthermore, organic carbon preservation strongly depends on the local circumstances of deposition (Hedges and Keil, 1995;Arndt et al, 2013), thus limiting the comparability of settings between regions and oceanic basins. There is an ongoing debate as to whether the proportion of organic matter, which is buried and preserved in marine sediments, is dependent on the ambient bottom-water oxygenation or not (Dale et al, 2014). The only assured perception is that carbon burial does not co-vary with bottom-water oxygenation at high sedimentation rates near continental margins (Betts and Holland, 1991;Canfield, 1994).…”

“…Even though this approximation includes many uncertainties, e.g. reliability of early sediment traps, variable burial efficiency (Dale et al, 2014), poorly constrained rates of Cretaceous primary production, it is reasonable to assume that part of the OAE 2 organic matter was lost during early diagenesis. It has to be emphasised that Holocene organic carbon accumulation rates in the centre of the Peruvian OMZ show a large scatter too, with maximum values of 6.8 g C cm −2 kyr −1 in core SO147-106KL, i.e.…”

Sources, Degradation, and Transport of Organic Matter in the New Britain Shelf‐Trench Continuum, Papua New Guinea

“…However, both landward sites and trench axis sites showed substantially higher rates of organic matter degradation compared to the abyssal sites. In order to quantitatively understand the spatial variations in the rates of organic matter degradation, we utilized the DIC flux at the sediment‐water interface to represent the rate of organic matter degradation considering that the DIC depth profiles were almost linear and DIC is the ultimate product of organic carbon oxidation (e.g., Anderson et al, ; Dale et al, ; Hulth et al, ). The calculated DIC fluxes were highest at the landward sites (NBT05 and NBT07) on both transects (Figure and Table ).…”