Oceanic Dead Zones
Fall 2012 , Lecture 9
Observing the Ocean
• Oceans cover about 70% of the earth’s surface
• Oceanography, the science of the ocean, has advanced
greatly in the last two centuries
• The video on the next slide is a production of the
Center for Ocean Science Education Excellence
(COSEE), and gives a brief view of how
oceanography is done today
2
Observing the Ocean
3
“Dead” Zones
• Some regions of the ocean may have, or develop, low
oxygen zones naturally
• One effect is the loss of marine life
 Mobile life forms, such as fish, leave
 Immobile forms often die
• Habitats that would normally be teeming with life
become, essentially, biological deserts, and are often
termed “dead zones”
4
Animal Oxygen Requirements
• Different organisms
have different
requirements for oxygen
• Fish, because they are
mobile, need more
oxygen than benthic
ogranisms
5
Effects of Hypoxia - 1
• Clams, oysters and other bivalves can survive for hours to
days by closing their shells, ceasing to filter water, and going
into a dormant state in hopes that normal oxygen conditions
will soon improve
• However, they too will die if hypoxia lasts long enough
6
Hypoxia Effects the Food Chain
• With initial lowering of oxygen concentrations, worms and
other animals that burrow deep in the mud will migrate closer
to the surface in search of more oxygen
• This makes them more vulnerable to fish that are capable of
surviving temporarily in low oxygen conditions
• Similarly, when fish and mobile invertebrates that rely on
hiding from predators along the bottom swim out of a hypoxic
area in search of more oxygen, they generally become more
vulnerable to larger fish that will eat them.
7
Natural Dead Zones
• Hypoxia occurs naturally in many of the world’s marine
environments, such as fjords, deep basins, open ocean oxygen
minimum zones, and oxygen minimum zones associated with
western boundary of many oceans where upwelling occurs
• Hypoxic and anoxic (no oxygen) waters have existed
throughout geologic time, but their occurrence in shallow
coastal and estuarine areas appears to be increasing as a result
of human activities
8
Hypoxia and Anoxia
• As we have seen, the scientific names for low oxygen
conditions are:
 Hypoxia - low levels of dissolved oxygen as the algae decomposes,
defined as dissolved oxygen ≤ 2.0 mg l-1
 Anoxia – Near zero oxygen levels, defined as dissolved oxygen <0.2
mg l-1
9
Permanent Hypoxia
• Some areas experience essentially constant hypoxia
10
Temporary Hypoxia
• In others, hypoxia lasts from hours to days
11
Seasonal Hypoxia
• Seasonal hypoxia occurs every year, during the warm months
12
Oxygen Solubility
• One important reason for
seasonal hypoxia has to do
with oxygen solubility
• Oxygen is more soluble in
cold water, and solubility
decreases as temperature
increases
13
Satellite Observation
• The Sea-viewing Wide Field-of-view Sensor
(SeaWiFS) can’t see the bottom of the ocean,
but it can see the surface, where sediments
from rivers mix with ocean water
14
Satellite Imagery
• The images shown here are
SeaWiFS observations of the
Mississippi River delta, the
Yangtze River mouth in China
(which is not currently identified
as an area with an associated dead
zone, but such conditions could
develop there in the future), and
the Pearl River mouth in China,
near Hong Kong
15
Dr. Robert Magnien
• Some of the information on the
following slides is from a
podcast with Dr. Robert
Magnien, Director of NOAA's
Center for Sponsored Coastal
Ocean Research
• Link is on the Information page
16
Anthropogenic Dead Zones
• There are many physical, chemical, and biological factors that
conspire to create dead zones, but nutrient pollution is the
primary cause of those created by humans
• Excess nutrients that run off land or are piped as wastewater
into our rivers and coasts can stimulate an overgrowth of
algae, which then sinks and decomposes in the water depletes
the supply available to healthy marine life
17
Worldwide Dead Zones
18
Location of U.S. Dead Zones
• Primary U.S. Oceanic Dead zones are found:
 Along the East Coast
 Along the Gulf of Mexico - the second largest dead
zone in the world is located in the northern Gulf of
Mexico
19
Northern Gulf of Mexico
• The Mississippi
River system is the
dominant source of
freshwater and
nutrients to the
northern Gulf of
Mexico.
20
Mississippi River Flow
• The discharge of the Mississippi River system is
controlled so that 30% flows seaward through the
Atchafalaya River delta and 70% flows through the
Mississippi River birdfoot delta
• About 53% of the Mississippi River delta discharge
flows westward onto the Louisiana shelf
21
Nutrient Pollution
• Mississippi River nutrient concentrations and loading to the adjacent
continental shelf have greatly changed in the last half of the 20th
century
• During this time there has been a marked increase in the
concentration of nitrogen and phosphorous in the Lower Mississippi
River
• This increase has been attributed to the increased use of nitrogen and
phosphorous fertilizers, nitrogen fixation by leguminous crops, and
atmospheric deposition of oxidized nitrogen from the combustion of
fossil fuel
22
Nonpoint Sources
• Nitrogen and phosphorous occur in four inorganic
forms in the river: nitrate (NO3-), nitrite (NO2-),
ammonium (NH4+), and orthophosphate (PO4-3)
• Many of these nutrients enter the river from non-point
sources like runoff, which are much more difficult
and complex to control and monitor than point
sources of pollution
23
Gulf Dead Zone History
• Hypoxia was first documented in the northern Gulf of Mexico
off the Louisiana coast in 1972
• Sporadic occurrences were observed in subsequent years
• In 1975 and 1976, two cruises were conducted specifically to
map a suspected area of low oxygen along the Louisiana coast
• These maps indicated small, disjunctive areas of hypoxia
• With an increase in oceanographic research in the Gulf of
Mexico, more reports of hypoxia emerged
24
Later Research
• The first concerted, continuous, and consistent documentation
of the temporal and spatial extent of hypoxia on the Louisiana
and Texas continental shelf began in 1985 with funding from
the National Oceanic and Atmospheric Administration,
National Ocean Service
25
CoSEE Dead Zone Video
26
Other Dead Zones in the U.S.
• The Great Lakes, particularly Lake Erie
• Chesapeake Bay
• There is no part of the country, or the world for
that matter, that is immune
27
Gulf of Mexico Dead Zone Size
• The size of the Gulf of Mexico dead zone
actually varies from year to year
• The average size, from 1993 to 2001, was
about the size of the state of New Jersey or the
states of Rhode Island and Connecticut
combined
28
Dead Zone Duration and Location
• As we saw in Chesapeake Bay, the duration of
the dead zone events varies from year to year
• The location also varies
29
Typical Dead Zone Scenario
• Most dead zones start to form in the spring,
most are severe in the summer, and then they
break up in the fall
• If spring rainfall is high, more nutrients can be
washed into coastal waters and that leads to
larger dead zones in that particular year
30
Winter Dead Zone Reset
• The zone is reset, in a way, each winter, when
seawater at the surface of the gulf gets cold and sinks,
bringing oxygen-rich water back to the hypoxic
bottom
• The following summer, the zone reforms, according
to Dr. Don Scavia, an aquatic ecologist with the
University of Michigan
31
Size Variation
• Its size varies from year to year, depending on how
much nitrate-rich water is being funneled toward the
sea from the Mississippi watershed, Dr. Scavia said
• For example, because of 2011Mississippi flooding,
last summer’s hypoxic zone was one of the larger
sizes recorded – more than two times this summer’s
32
Hurricane Effects
• Any oceanic region affected by a hurricane,
such as the Gulf of Mexico, hurricane driven
mixing can stir up the water sufficiently to reoxygenate the bottom water, even in summer
• Usually the dead zone reforms in about one to
two weeks
33
Dead Zone Invisibility
• From the surface, most dead zones are
invisible
• Diving into hypoxia zones, or using remote
cameras, can sometimes reveal their presence
• Factors leading to dead zone formation, such
as large algal blooms, are visible
34
Dead Zone Numbers
• The number of dead zones has greatly
increased since the 1960’s
• Over 400 dead zones worldwide have been
documents
• In the U.S., 166 have been documented
35
Economic Impacts
• Exact economic impacts are largely unknown
• In 2009, the Gulf of Mexico fisheries
amounted to about $2.8 billion
• How much was lost to the dead zone has yet to
be quantified
36
Research Efforts
• The Center for Sponsored Coastal Ocean Research in
the National Ocean Service spent $27 million over 15
years on hypoxia research
• That produced a Management Action Plan, first
issued in 2001 and revised in 2008
• They issue seasonal predictions of the dead zones in
the Gulf of Mexico and Chesapeake Bay
37
Recent Episodes
• Chris Paschenko reported in The
Galveston Daily News on
August 13, 2012, “Low oxygen
levels are believed to have killed
possibly hundreds of thousands
of Gulf menhaden fish found
littering beaches and shorelines
from Matagorda to Galveston,
officials said Sunday.”
(August12)
38
Why Menhaden?
• Gulf menhaden, also known as shad, are more susceptible to
fish killings than other species
• Steven Mitchell, a biologist with the Texas Parks and Wildlife
Department, said “Menhaden swim in the thousands of fish in
schools, and when they get into trouble, they just can’t get out
of it. I suspect the schools were swimming in a dead zone
offshore, but we haven’t confirmed that.”
39
Red Tide Responsible
• Low to moderate concentrations of red tide, an algal bloom
known as Karelia brevis, also were believed to have caused
fish kills in Galveston Bay
• The presence of the algae prompted the Texas Department of
State Health Services on Monday to close what little oyster
harvesting was ongoing by public lease holders in Galveston
Bay, department spokesman Chris Van Deusen said
• Oysters are harvested commercially in Texas only from
November to April
40
Galveston Fish Kill
• Stan Lewis of Dallas rakes
dead fish away from his
family’s tent at Bermuda
Beach in Galveston on Sunday
• Officials said a red tide could
be responsible for the fish kill
• Photo by Jennifer Reynolds
41
Dead Zone and Drought
• NOAA-supported scientists have found the size of the
2012 Gulf of Mexico oxygen-free ‘dead zone’ to be
the fourth smallest since mapping of the annual
hypoxic, or oxygen-free area began in 1985
• Measuring approximately 2,889 square miles, the
2012 area is slightly larger than Delaware
42
Dead Zone Variation
• Scientists supported by the National Oceanic and Atmospheric
Administration (NOAA) have been monitoring the size of the
Gulf of Mexico dead zone since 1985
• From 1985 to 1992, the extent of the summer dead zone
averaged about 3089 to 3475 square miles
• From 1993 to 1997, the size of the dead zone had grown to
6178 to 6950 square miles
• The largest dead zone ever recorded occurred in 2002 and
measured 8400 square miles
43
Gulf of Mexico, 1985-2011
• In 2012, it was 2889 mi2
44
Control of Fertilizer Input
• The small 2012 dead zone suggests that a
reduction of nitrate input into the Gulf of
Mexico would have an immediate impact
• In addition to controlling the agricultural and
home inputs of fertilizer, is there another way
of reducing dead zones?
45
Natural Fertilizer Buffers
• Dr. Scavia has two suggestions:
 Building wetlands around the rivers would
encourage the natural denitrification that occurs in
such ecosystems
 Buffering rivers with grasses to absorb the nitrates
would also help
46
Environmental Activism
• Green groups have been trying to persuade the
Environmental Protection Agency (EPA) to set a limit
for the amount of nitrogen and phosphorus allowed in
the states whose rivers feed the Mississippi
• In March, 2012 members of the Mississippi River
Collaborative, an environmental group, filed a lawsuit
designed to force all those involved to think about
ways to solve the problem
47
Environmental Pushback
• The Federal Water Quality Coalition, a group
composed of industrial and metropolitan water users,
has launched its own lawsuit in opposition to the first
• It argues that the federal government should play no
role in setting limits, and furthermore that the very
idea of limits is too simplistic
48
State Action
• Wisconsin is one of the few states to introduce,
in 2010, statewide numerical limits for
phosphorus
• Joe Parisi, who runs Dane County, says these
have spurred the county into working on new
measures with the Madison metropolitan
sewerage district
49
State Ideas
• Wisconsin has suggested two ideas
 One is an innovative community biodigester that
generates power from cattle manure
 Another idea is a low-tech effort to extract
phosphorus by using crops which are then
harvested
50
Upstream Problems
• The effects of nutrient pollution are
increasingly apparent throughout the
Mississippi River basin
• Environmentalists say that half the streams in
the upper Mississippi have too much nitrogen
and a quarter have too much phosphorus,
according to an article in The Economist
51
Effects Upstream from the Gulf
• Nutrient enrichment damages aquatic life along the
rivers and streams in the Mississippi watershed, and
degrades drinking water quality
• Blooms of toxic algae have closed beaches, made
people ill and killed fish and pets along various rivers
• Nasty green lakes have also damaged tourism,
property values and fisheries
52
Dead Zones and Climate Change
• Dr. Lou Codispoti, University of Maryland
Center for Environmental Science
oceanographer, has produced research showing
that hypoxic zones in the ocean can contribute
to the release of nitrous oxide (N2O), a
powerful GHG
53
N2O Production
• Dr. Codispoti found that the yield of N2O increases
twenty-fold between water saturated with oxygen and
water at 1% oxygen saturation
• He states that net N2O production in the open ocean is
about 6 Terragrams of N per year, and half is from
hypoxic and suboxic waters
• Estuaries produce an additional amount, about half
that of the ocean
54
Shallow Waters
• He says, “N2O production rates should be
particularly high in shallow suboxic and
hypoxic waters, because respiration and
biological turnover rates are higher near the
sunlit waters where phytoplankton produce the
fuel for respiration”
55
Enhanced GHG
• Thus, increasing inputs of nitrogen fertilizers
into shallow estuarine or coastal shelf waters
will contribute substantially to enhancing a
powerful GHG
56
Other Sites Around the world
• Hypoxia is not limited to the United States
• We will look at two other cases
 Black Sea
 Baltic Sea
57
Black Sea
• This large, inland sea has also
been affected by humans for
centuries
• Nutrients entering the system
from rivers like the Danube began
to increase sharply in the 1960s,
causing an increasing dead zone
on the northwestern part of the
Black Sea
58
Black Sea Improvement
• This anthropogenic dead zone was an addition to the
permanent dead zone that exists in the deepest parts of the
Black Sea
• After the Soviet Union collapsed in 1989 a rapid slowdown of
intensive farming and the large-scale raising of livestock in the
Danube watershed caused great reductions in the amount of
nutrients entering the northern Black Sea
59
Northwestern Black Sea
• Bt the mid-1990’s, the dead
zone of the Northwestern
Black Sea all but disappeared
• This gives hope that large
reductions in nutrient load
will indeed reduce the
frequency and extent of dead
zones
• High nutrient loads cause major
phytoplankton blooms on the
Black Sea
60
Nutrient
Loading
• The diagram
shows the effect
of nutrient loading
61
Baltic Sea
• This northern European body of
water is a salty, deep system that
has been affected by humans for
centuries
• Following World War II, increasing
fertilizer use and a growing
population led to high inputs
of nutrients to the system from
rivers like the Oder and the
Vistula.
62
Baltic Sea Decline
• As happens in many marine systems, this increased
nutrient load caused algae blooms which eventually
caused low oxygen conditions
• Efforts to decrease nutrient loads to the Baltic were
successful in minimizing the size of the dead zone in
the mid-1990s
• Unfortunately, climatic conditions have caused dead
zone area to increase again in recent years
63
Baltic Sea
Hypoxia Area
• Decreases in
nutrient loading
helped
64
Baltic Sea Stratification
• The Baltic Sea water is stratified - density differences of changing
water temperature creates a seasonal thermocline, a layer where
temperature rapidly changes
• The strongest thermocline exists in the summer when warmed
surface water separates from colder bottom water
• Summer thermocline usually exists in approximately water depth
of 10-20 meters
• In warm summer weather the surface temperature can rise up to
20-22 °C, while the bottom water under the thermocline stays at 35 °C
65
Baltic Thermal Conditions
• The summer stratification is evident
66
Climate Change Effect
• The thermal stratification in summer leads to
an anoxic zone in deep water
• As climate change heats summer waters, the
stratification begins earlier and lasts longer
67
Baltic Ice Cover
• Annual size of the Baltic Sea ice cover
since the 1700s based on various types of
observations
• The annual variation is large, but the
variations are considerably smaller when
illustrated as 30-year mean values (red
curve)
• The green line shows the average size of
the ice for the entire period and the circle
marks a breakpoint where the climate
changed and the Little Ice Age ended
68
Deepwater Horizon
• Deepwater Horizon was an ultra-deepwater,
dynamically positioned, semi-submersible offshore
oil drilling rig
• In September 2009, the rig drilled the deepest oil well
in history at a vertical depth of 35,050 feet (10,683
m) and measured depth of 35,055 feet (10,685 m)
approximately 250 miles southeast of Houston, in
4,132 feet (1,259 m) of water
69
Deepwater Horizon Explosion
• On April 20, 2010, while drilling at the Macondo
Prospect, an explosion on the rig caused by a blowout
killed 11 crewmen and ignited a fireball visible from
35 miles away
• The resulting fire could not be extinguished and, on
April 22, 2010, Deepwater Horizon sank, leaving the
well gushing at the seabed and causing the largest
offshore oil spill in U.S. history
70
Deep Horizon Fire Video
71
Capping the Well
• The gushing wellhead was capped, after it had
released about 4.9 million barrels (780,000 m3) of
crude oil, on July 15, 2010
• On September 19, 2010, the relief well process was
successfully completed, and the federal government
declared the well “effectively dead”
72
Persistent Problems
• In August 2011, oil and oil sheen covering several square
miles of water were reported surfacing not far from BP’s
Macondo well, but the oil was too dispersed to recover
• Scientific analysis confirmed the oil is a chemical match for
Macondo 252
• The Coast Guard said the oil In March 2012, a "persistent oil
seep"near the Macondo 252 well was reported
73
Early Scientific Observation
• “There’s a shocking amount of oil in the deep water, relative to
what you see in the surface water,” said Samantha Joye, of the
Institute of Undersea Research and Technology at the
University of Georgia who is involved in one of the first
scientific missions to gather details about what is happening in
the gulf. “There’s a tremendous amount of oil in multiple
layers, three or four or five layers deep in the water column.”
(Quoted from article by Justin Gillis, N.Y. Times, May 15,
2010)
74
Methane Emission
• One early concern about the oil spill was the amount
of methane associated with the petroleum
• John Kessler, a Texas A&M University
oceanographer, said that the oil emanating from the
seafloor contains about 40 percent methane,
compared with about 5 percent found in typical oil
deposits
75
Dissolved Methane
• A BP spokesman said the company was burning about 30
million cubic feet (850,000 cubic meters) of natural gas daily
from the source of the leak
• In early June, a research team led by Samantha Joye
investigated a 15-mile-long plume drifting southwest from the
leak site
• The team reported methane concentrations up to 10,000 times
higher than normal, and oxygen levels depleted by 40 percent
or more
76
Methane Dead Zone
• Joye’s research team found that some parts of the plume had
oxygen concentrations just shy of the level that tips ocean
waters into the category of "dead zone" — a region
uninhabitable to fish, crabs, shrimp and other marine creatures
• John Kessler’s research team found similar results - he said he
has already found oxygen depletions of between 2 percent and
30 percent in waters 1,000 feet (300 meters) deep.
77
Oxygen Depletion
• Small microbes that live in the sea have been feeding on the
oil and natural gas in the water and are consuming larger
quantities of oxygen, which they need to digest food
• As they draw more oxygen from the water, two problems
result
 When oxygen levels drop low enough, the breakdown of oil grinds to a
halt
 As oxygen is depleted in the water, most life can't be sustained
78
Dispersants
• British Petroleum treated the spill with very
large quantities of dispersants
• Dispersants are chemicals designed to attach to
oil molecules and to water molecules, making
the petroleum much more soluble in seawater,
and helping to break the spill into many tiny
droplets
79
Invisible?
• Small droplets are easier for microbes to attach
and break down the petroleum
• Of course, breaking up the petroleum and
getting it into the deep water column make it
much less visible at the surface…..
80
Dispersant Toxicity
• Many dispersants are quite toxic, and
biologists fear they could cause increased
marine mortality, leading to chemical dead
zones
81
Dispersant and Petroleum Quantities
• BP used 1.8 million gallons of Corexit
dispersant
• It is believed that a lot of the estimated 200
million or more gallons of oil that spewed out
of the blown well remains under the surface of
the Gulf in plumes of tiny toxic droplets
82
Dispersant in Crabs
• Scientists have found signs of an oil-and-dispersant mix under
the shells of tiny blue crab larvae in the Gulf of Mexico
• Harriet Perry, a biologist with the University of Southern
Mississippi's Gulf Coast Research Laboratory, said marine
biologists started finding orange blobs under the translucent
shells of crab larvae in May, and have continued to find them
"in almost all" of the larvae they collect, all the way from
Grand Isle, Louisiana, to Pensacola, Fla. -- more than 300
miles of coastline
83
Dispersants as Delivery Systems?
• "Corexit is in the water column, just as we thought, and it is
entering the bodies of animals. And it's probably having a
lethal impact there," said Susan Shaw, director of the Marine
Environmental Research Institute. The dispersant, she said, is
like " a delivery system" for the oil.
• "The properties that facilitate the movement of dispersants
through oil also make it easier for them to move through cell
walls, skin barriers, and membranes that protect vital organs,
underlying layers of skin, the surfaces of eyes, mouths, and
other structures."
84
Waiting for Answers
• This is a clear indication that the
unprecedented use of dispersants in the BP oil
spill has broken up the oil into toxic droplets
so tiny that they can easily enter the foodchain
• What the longer term effects of Corexit and
petroleum on life in the Gulf will be await
years of on-going research
85
ROV’s
• On October 18, 2012, remote operated vehicles
(ROV’s) deployed from the offshore
construction vessel Skandi Neptune collected
oil samples from the underwater site of the
Deepwater Horizon incident to determine the
source of a surface sheen discovered last
month
86
Oil Samples
• Samples were taken after the ROV video showed apparent oil
globules leaking from the containment dome at approximately
15 globules per minute, which is estimated to be less than 100
gallons per day
• In 2010, the 40‐foot‐tall containment dome was used as part of
an attempt to capture oil and allow it to flow through a pipe to
a barge on the surface
87
Containment Dome
• This technique was not successful and the equipment
was moved away from the well head and riser pipe,
and set in its current position approximately 500
meters from the original Macondo well head
• It is entirely separate from the well head and any riser
piping
88
Recent Work
• The Federal On-Scene Coordinator for the Deepwater Horizon
oil spill in New Orleans authorized BP to proceed with a plan
to cap and plug the containment dome on 10-25-12
• The technique was unsuccessful and the equipment was moved
away from the well head and riser and set in its current
position approximately 500 meters from the original Macando
well head
89
BP Deep Horizon 2nd Anniversary
• CBS News report - April 20, 2012
90