Biomass depletion in the big picture
buddrw at kgs.ukans.edu
Fri May 25 18:34:49 EDT 2001
1. Fossil fuel emissions:
"Since 1751 over 270 billion tons of carbon have been released to the
atmosphere from the consumption of fossil fuels and cement production. Half of
these emissions have occurred since the mid 1970s. The 1997 estimate for global
CO2 emissions, 6601 million metric tons of carbon, is
the highest fossil-fuel emission estimate ever."
2. Global fishery production is cited by McGinn (1998) in Worldwatch Paper 142
as rising from 20 million tons in 1950 to about 120 million tons in the mid
1990s. This is in tons of wet weight biomass, which is typically on the order
of 1% carbon. Even with a generous estimate of 5% C/wet weight, annual fishery
removal from the sea is <0.1% of the annual fossil fuel input to the
3. If one assumes that most of the biomass extraction is at least two steps up
the food chain from the primary producers, the "factor of 10 per trophic level"
rule of thumb suggests that fisheries deplete total marine biomass by no more
than 1%. This is probably a significant overestimate.
4. Human acceleration of nutrient cycles has led to major eutrophication in
many coastal areas (which are disproportionately important to the total marine
productivity) -- this is production of EXCESS marine biomass at the most basic
and quantitatively dominant level.
5. A review of the carbon cycle literature shows that the biggest scientific
challenge is the identity of a "missing" carbon sink. If fishery depletion
were actually making an unrecognized contribution to the atmospheric CO2, this
would be a missing source, not a sink.
>From all of the above, I conclude that "a strong case" CANNOT be made that
"fishing has made a large contribution to the rise in atmmospheric CO2."
I hope that counterarguments will be put forward quantitatively, in terms of
the extensive literature on global carbon inventories and dynamics.
Debbie MacKenzie wrote:
> Hi Coral-list,
> The discussion on the causes of mass coral bleaching has been very
> interesting, thanks, but I've still not gotten answers to two of my main
> questions: Do you see a physical difference between what happens in mass
> bleaching events and what you would expect to see in food starvation? - and
> - Do you have any time-series data on the abundance of tropical ocean
> zooplankton? A strong case can be made that fishing has made a large
> contribution to the rise in atmospheric CO2.
> Debbie MacKenzie
> An increase in atmospheric CO2 is an expected consequence of removal of the
> marine biota. It is demonstrated that the progressive fishing-induced
> biomass depletion of the worlds ocean is a more plausible explanation for
> what has triggered the rising CO2 in the atmosphere, than is our more
> recent history of burning fossil fuels. Proof for the long-term trend in
> biomass depletion is found by examining the contrasting pictures of
> abundant marine species pre-fishing and the life-depleted status of the
> worlds ocean today. The realization that biomass depletion has bottom-up
> effects as well as top-down ones leads to the inevitable conclusion that
> marine primary productivity is functioning at a significantly lower level
> now than it did in the past, when the ocean-atmosphere maintained a steady
> carbon balance.
> Humans cannot remember the great abundance of sea life that existed even
> 500 years ago...but the ocean can. Deep water circulation patterns today
> bring carbon to the surface in ocean upwelling areas, in the same manner
> and quantity as they always have. This carbon is exhaled to the
> atmosphere in a process known as outgassing. What comes out of the sea is
> very old carbon, the memory of marine primary production that took place
> centuries ago. The deep water contains a vast pool of carbon, and it
> circulates only very slowly; the average turnover time may be about 1000
> years. For many thousands of years the ocean and atmosphere maintained a
> carbon balance, and atmospheric levels were steady, but no longer. New
> carbon cycled into the deep water annually balanced the amount that was
> cycled out...but a rather long lag time exists between the two. Due to the
> drop in marine primary productivity, todays carbon input to the deep water
> falls significantly short of what is required to balance the amount that
> the ocean sends out via outgassing. Due to the 1000 year lag time between
> the input and output ends of the cycle, readjustment will take a while. The
> ocean and atmosphere are seeking a new state of carbon balance. The amount
> of CO2 exhaled annually by the ocean today represents the average amount of
> carbon put into the deep pool on a yearly basis over the last 1000 years.
> Due to the fishing-induced imbalance, CO2 levels in the atmosphere are
> rising. For the past two centuries the sea has exhaled larger amounts of
> CO2 than it has inhaled. This is an unrecognized consequence of human
> fishing, and continued fishing will only exacerbate the situation.
> For directions on subscribing and unsubscribing to coral-list or the
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Dr. Robert W. Buddemeier
Kansas Geological Survey
University of Kansas
1930 Constant Avenue
Lawrence, KS 66047 USA
Ph (1) (785) 864-2112
Fax (1) (785) 864-5317
e-mail: buddrw at kgs.ukans.edu
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