University:
Widener University
Course:
CHEM-255 | Organic Chemistry I
Academic year:

2023
Views:

115

Pages:

38
Author:

maegeshoqay

If the ocean is so efficient in remineralizing C and nutrients, why is C preserved at all in sediments? Organic Carbon (wt. %) 0 0.0 1.0 2.0 3.0 Interglacial Glacial Depth (cm) 40 P6 P2 80 Glacial Interglacial 120 160 Organic carbon with depth in late Pleistocene sediments from the eastern Equatorial Pacific Ocean. (Pederson and Calvert, AAPG Bull.(1990) v74, 454-466). Sapropels organic rich (2-14% TOC) Periodic deposition <1 cm to > 10 cm thick Nonsapropels Very organic lean (0.1% TOC) Most of the deposition Sapropels Any organic rich layer of sediment is called a sapropel, Sapropels in the Medditerranean Sea are very interesting however because the Med is one of the least productive bodies of water today, and sedimetns there are extremely depleted in organci carbon. A very long historical record of sapropel deposition was collected by the Ocean Drilling Program Legs 160 and 161 (see Initial reports…). Sapropels were first discovered in the Eastern Mediterranean Sea, but ODP found them to be synchronous in both basins. The shallowest sapropel is < 1m deep and can be sampled with a gravity core. Correlation between 440C and nitrogen isotopes in Mediterranean Sea sediments The effect of oxygen on carbon preservation in Maderia Abyssal Plain Turbidites Before… During… and Voila! The effect of oxygen on carbon preservation in Maderia Abyssal Plain Turbidites Correlation between 440C and nitrogen isotopes in Mediterranean Sea sediments What causes sapropels to form in the Mediterranean Sea? And more generally, what processes act to preserve carbon In marine sediments? Enhanced productivity due to Inputs of nutrients? or Enhanced preservation due to Bottom water anoxia? The productivity vs preservation debate CP factor #1. The argument for productivity…… Relationship between O h OC and sedimentation rdte 0. I 1.0 10 I'00 I0010 Sedimentation rate (mg cm-2 y-I] Relationship between burial efficiency and sedimentation rate 0.OOQI 0.001 O"01 0.1 1 10 Sedimentation rate (crn/y) Effect of bottom water oxygen on burial efficiency 100 Bottom water oxygen {MI Hartnett et al. (1998) Nature v391, 572-574 The effect of oxygen has been refined somewhat to adjust for differences in exposure time, which is related to sedimentation rate (depth of O2 penetration/sedimentation rate) = OET Is carbon more efficiently respired under oxic or anoxic conditions ? Is carbon more efficiently respired under oxic or anoxic conditions ? spring winter Oxi$atiom rate and the lability of organic carbon Lability of organic carbon (ma1dm'g'l) CP Factor #3 The composition of organic matter Was the compostion of OM in anoxic sediments different than the OM in oxic sediments, thereby producing the Observed difference? Is the “G” model just and observational artifact? The Carbon Preservation Quiz ! T F Productivity affects carbon burial efficiency. Relatively more carbon is buried under anoxic than oxic conditions. Bigger molecules are degraded more slowly than smaller molecules. The faster you bury carbon, the more likely it is to stay buried. Carbon preservation summary Ocean is >99.5% efficient at recycling C. Annual production is about 50-70GT C yr-1, of which 0.1-0.2% is buried. Several factors affect C preservation: organic matter production oxygen organic matter composition It is difficult to isolate these factors from one another to elucidate underlying mechanisms