Introduction to Aquatic and Marine Geochemistry
Introduction to Aquatic and Marine Geochemistry EPS 103
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This 5 page Class Notes was uploaded by Adele Hoeger on Thursday October 22, 2015. The Class Notes belongs to EPS 103 at University of California - Berkeley taught by J. Bishop in Fall. Since its upload, it has received 27 views. For similar materials see /class/226574/eps-103-university-of-california-berkeley in Earth And Space Sciences at University of California - Berkeley.
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Date Created: 10/22/15
Iron a global perspective Lecture given on 102600 EPS 103203 Intro to Marine Geochem The goal of this lecture was to fill in some of the gaps in your knowledge of iron s role in ocean fertilization In order to do this I introduced you the idea of the biological pump in the ocean and its role in reducing atmospheric carbon dioxide Part 1 The biological pumn I What is the biological pump Biologic activity in particular primary productivity draws in C02 from the surrounding water column Dead organisms will sink in the water column Some of it will remineralize and some will continue below the thermocline That material that makes it below the thermocline is effectively sequestered from the surface ocean thereby completing the pumping of atmospheric C02 into the deep ocean I What does the pump affect Global climate perhaps and carbon ow Locally 0 CO2 levels Also 0 CH4 N20 and DMS 30 to 40 of fossil fuel C02 goes into oceans Small perturbations to the system can have large ramifications Controls 0f QCOg ocean I Inorganic controls Carbonate equilibriaspeciation Carbonate precipitation and dissolution Global circulation patterns Solar heating and upwelling of C02rich waters Where are the available sinks for CO2 in the ocean I 0rganic controls Removal by photosynthesis biosynthesis of carbonate shells Addition by oxidation of organic matter 7 A complicating issue is that heterotrophic bacteria respire C02 when they catabolize organic compounds I then explained why iron is critical to organisms and introduced you to iron profiles in the ocean The latter was intended as an introduction to cycling of F e in the water column This was carried further in a later section by talking about modes of iron transport to the ocean Overall the goal of this section was to piece together the iron cycle in the framework of iron s importance to organisms in the ocean Part II uestions I Does iron limit the growth of organisms Fe m be limiting in the ocean Increasing Fe would increase primary production which would increase C02 drawdown gt biological pump I In which metabolic processes is iron important Iron a global perspective Lecture given on 102600 EPS 103203 Intro to Marine Geochem I How does iron limitation affect metabolism and growth Iron physiology I Fe is an essential micronutrient Focus on two pathways that need iron Photosynthesis e g photosynthetic reaction centers Nitrogen xation e g nitrogenase reductase Fe can also be used as Electron donor Anoxygenic photosynthesis Terminal electron acceptor Anoxic respiration In proteins of electron transport system How does this relate to the ocean I Hypothesis Organisms need iron to grow l m Where is iron limiting Do we see evidence for limited growth Does the addition of Fe to limited regions promote growth How does this growth affect pCOz Fe pro les in the ocean I Nutrientlike I No interocean fractionation Unique for nutrient element I Little scavenging at depth Strange for trace metal compare to Pb Only operates at conc gt solubility levels I Residence time S 100200 yrs fast Circulation time of ocean Z 1000 yrs HNLC regions of the ocean I Equatorial Paci c Ocean subarctic Paci c and Southern Ocean High nutrients NOg39 PO439 low chlorophyll Low atmospheric input of Fe I Causes of low phytoplankton biomass Grazing pressure by herbivores Slow production Nutrient andor light limitation In situ iron fertilization I Pour some Fe into the ocean as FeSO4 Iron a global perspective Lecture given on 102600 EPS 103203 Intro to Marine Geochem Mixed results IronExI 51gt Small 0 in fcoz in patch IronExII repeatedly add Fe 51gt Larger 0 in fcoz 90 uatm gradient between outside and inside of patch Integrated drawdown 285108 g C Apcoz 150 to 60 uatm Increased photosystem ef ciency DMS Altered photosynthetic apparatus IronEx in the e uatorial Paci c Date Oct 93 May 95 Location Equatorial Pacific Target concentration nM 2 nM Size ofpatch 64 km2 72 km2 pCO uatm 13 73 Chlorophyll lg l 041 39 Primary Production 1 8 ll 6 Mg C F dayquot 02 M 28 32 Nitrate M 07 4 Phosphate M 002 025 Table 1 Changes in chemistry of ocean patch after the addition of iron during IronEx I one enrichment and Iron EX II three enrichments From Steinberg et al 1998 Marine Chemistry 62 31 43 Fluorescence of photosystem II can be used to determine the ef ciency with which photosynthetic organisms utilize incoming light to form biomass I All RCs oxidized F0 light hits chlorophyll Molecule is excited Energy transferred to other molecules photochemistry or released Release heat assume 0 uorescence gtgt Fluorescent molecule is lower energy higher wavelength can be measured All RCs reduced Fm no more e transport Physiological effects of increased Fe in the photic zone I Photochemical uantum ef ciencies F0 minimum uorescence Fm uorescence in the lightsaturated state kp 0 FV variable uorescence Where EA Fm F 1 F 7 F is the equation used to calculate quantum ef ciency the ef ciency with which light is absorbed by PSIIassociated chlorophyll molecules I If you model the Southern Ocean as Peng and Broecker 1991 did you can put some Iron a global perspective Lecture given on 102600 EPS 103203 Intro to Marine Geochem limits on the effect of iron fertilization 7 Basically the authors created two endmember box models which simulated the movement of water in the Southern Ocean Then they fertilized the region for 100 years this was done by assuming that in such a regime all of the phosphate would be utilized by growing organisms Using a Redfield ratio you can figure out how much carbon that represents and estimate how that carbon would be sequestered given the two scenarios I Has natural Fe fertilization occurred in the past If so where did the iron come from We need some background on this question so we will consider the natural abundance of iron and iron transport in the natural environment Fe Ppb Crustal average 50105 Granite 137106 Diabase 776106 Shale 38106 Sandstone 186106 Carbonate 082106 Ore deosit gt250106 Acid mine drainage 011106 I How does iron input increase to account for past climate change What geological processes can we invoke And what are the longterm effects What are the relative timescales of interest Recycling subduction zones N 10 a Natural climate cycles 105 40000 and 20000 a Mixing time ofthe ocean 1000 a Phytoplankton turnover times days Fe transport to the oceans I Aerial deposition Mainly open ocean as dust in aerosol particles I Fluvial deposition By rivers through estuaries into coastal ocean Dissolved and colloidal forms Conservative mixing or removal by occulation and gravitational settling Fe behavior in zones of mixing I Is iron removed is estuarine envts a What happens to iron as it moves from fresh to saltwater a Boyle 1977 50 to 95 removal 7 Gustafsson 2000 Iron a global perspective Lecture given on 102600 EPS 103203 Intro to Marine Geochem Little to no removal during spring ood I Aggregation definitely occurs 7 Salinity vs dilution 7 Which is more important increasing salinity means more electrolytes in solution which means a greater shielding of surface charge on Fe oxides This allows for aggregation of small particles to occur However increasing the mass of water has the opposite effect by increasing the distance a colloid has to travel before it collides with another colloid Transport off the shelf can occur as Bishop and Wood unpublished data demonstrated off the west coast of North America Redox processes play a role in both Mn and Fe release from the shelf and slope into the open ocean Hydrothermal inputs of Fe may be important in surface processes although this is not well understood Regardless of this point iron is released at deep sea hydrothermal vents and ridges as both dissolved ferrous 11 iron and particulate ferric III iron I then spoke about iron isotopes and their potential for use in the marine system These are just my ideas and research and so I have not included that here
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