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COMMENCE. ANTHROPOCENE COASTAL OCEAN CARBON-CARBONATE SYSTEM Fred T. Mackenzie 1, 2 Andreas Andersson 1 , Katie Fagan 1 , Dan Hoover 1 , Abraham Lerman 2 , Stephanie Ringuet 1 1 University of Hawaii; 2 Northwestern University. OUTLINE I. Introduction

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ANTHROPOCENE COASTAL OCEAN CARBON-CARBONATE SYSTEMFred T. Mackenzie1, 2Andreas Andersson1, Katie Fagan1, Dan Hoover1, Abraham Lerman2, Stephanie Ringuet11University of Hawaii; 2Northwestern University



I. Introduction

II. Modeling the coastal ocean CO2-carbonic acid system, air-sea CO2 exchange, and effects of rising atmospheric CO2 and temperature on coastal seawater carbonate saturation states and calcification and carbonate mineral dissolution rates during the Anthropocene

III. Coastal ocean air-sea exchange of CO2 and carbonate saturation state: Lessons on variability from Hawaiian and other coastal ecosystems


In contrast to the open ocean, little attention has been given to the role of the shallow coastal ocean in the carbon cycle and its modeling in the context of global change despite the fact that:

  • 8% of the global surface area of the oceans and 2-3% of the volume of the open ocean surface layer reside there
  • 80% of river terrigenous input containing reactive nutrients of N and P and organic carbon is deposited in this region
  • Accounts for 10-30% of global organic primary production
  • Site of 85% of global organic carbon burial
  • Accounts for 26% of global inorganic carbon production, mainly of metastable skeletal aragonite and magnesian calcites
  • Site of 45% of global inorganic carbon burial (reefs account for about 22%); most accumulation of shoal-water CaCO3 is in the southwest Pacific Ocean
  • Globally still appears to be a source of CO2 to the atmosphere
  • Heavily impacted by human activities, including doubling of the nutrient N and P and total organic carbon river fluxes since pre-industrial time


We have used two models to investigate the Anthropocene history (past few centuries and future) of the global coastal ocean and carbonate ecosystems. These are:

TOTEM--Terrestrial Ocean-aTmosphere Ecosystem Model and

SOCM--Shallow-Ocean Carbonate.

Both models are complex renditions of the carbon (and nitrogen and phosphorus) biogeochemical cycles and their physical, chemical and biological dynamics in the global coastal ocean. Equations for organic productivity, organic respiration, carbonate precipitation and dissolution and temperature and carbonate saturation effect on the rates of carbonate precipitation are part of the SOCM.

Depending on the question asked, these two models can be


The major forcings in the models are:


Model forcings

based on history

from 1700 to early

21st century, BAU to 2100 and linear

extrapolation to



Coastal ocean surface and pore water carbonate saturation state for different IPCC scenarios of CO2 and T


Marine carbon

chemistry and seawater saturation state of the coastal ocean with respect to various carbonate minerals


Carbonate saturation state as a function of latitude (T and DIC); Notice problem with Mg-calcite pKs and the fact that rising CO2 and temperature may affect high latitude and temperate cold-water carbonate ecosystems to an extent perhaps greater than subtropical/tropical reef ecosystems


Calcium carbonate production and dissolution in the coastal

ocean using different relationships for the effect of carbonate

saturation state and temperature on calcification rate


Pore water CaCO3

saturation state, CaCO3

dissolution flux and organic matter sedimentation and remineralization fluxes in coastal ocean sediments



  • The global coastal ocean, including most reef ecosystems, probably is still a net source of CO2 to the atmosphere but soon will become a net sink with rising atmospheric CO2. Estuaries have a high area specific air-sea CO2 exchange of -35.8 mol C m-2 y-1 vs +1.17 mol C m-2 y-1 for the distal coastal zone.
  • Both models and observational data show declining carbonate saturation state for the world oceans, including its coastal ocean waters.
  • Modeling shows that saturation state with respect to calcite could decline 45% by the year 2100 and 70% by the year 2300 in coastal ocean waters. Carbonate dissolution and production of alkalinity will not be sufficient enough to buffer the decline in saturation state.
  • The CaCO3 production rate in coastal seawater could decrease as much as 40 % in the year 2100 and 90% in the year 2300 because of decreasing saturation state and rising temperature.




  • A significant portion of the area of estuaries of 1 x 1012 m2 of the world is found in the tropical/subtropical climatic zone. A number of these systems have coralgal reefs associated with them, like Kaneohe Bay, Hawaii.
  • No extended time series studies of the marine carbon system and air-sea exchange of CO2 have been performed in the coastal zones of tropical/subtropical environments, including reefs.


Bimonthly sampling of surface waters at 23 sites for marine carbon parameters since September, 2003.

Total alkalinity and dissolved inorganic carbon analysis done

using the Hawaii Ocean Time-series program equipment and

analytical protocol.

PCO2 calculated using constants from Mehrbach et al. (1973) refit

by Dickson and Millero (1987).

Additional data for physical properties of the bay (T, S, wind

speed and direction, sunlight), river discharge and river and bay nutrient and organic carbon concentrations, dissolved oxygen concentrations, bay productivity, standing crop and phytoplankton community structure, turbidity, etc. were collected through the course of the work.


Diel variability of marine carbon system, Mangrove Bay, Bermuda fringing and back-reef Thalassia grass and calcareous green algae biome



  • Majority of estuaries and “ecological” reefs studied to date have been shown to be sources of CO2 to the atmosphere presently.
  • Estuary and reef ecosystems are extremely dynamic on very short time scales and the direction and magnitude of the air-sea exchange flux and the carbonate saturation state can change rapidly thus:
  • There is a strong need for time series data for the coastal ocean marine carbon system, involving at least two carbon system variables to calculate all carbon system parameters, including carbonate saturation state. Complementary physical and biological data are also needed where possible.

Average PCO2s

variable and

strongly affected

by storm runoff

from streams: enhanced productivity draws down CO2 after initial input of high PCO2 stream waters


Storms strongly

affect proximal

zone PCO2s and hence carbonate saturation state due to river runoff

flushing out high

PCO2 soil and ground waters


Baseline and temporal changes in nutrient and chlorophyll-a concentrations during a storm event: storms bring in nutrient-rich waters with high N/P ratio and promote productivity


Productivity, Chl-a and TSS during a storm event: productivity enhanced by input of nutrient-rich river waters after bay waters clear and sun comes out


Temporal changes

in Chl-a, pigments

and pigment ratios

during a storm event: the phytoplankton

community shifts from one dominated by small diatoms,

cyanobacteria and chlorophytes to one dominated by large, chain-forming and pennate diatoms


Reminder: organic C and

inorganic C

coastal zone cycles

are coupled