Climate scientists are
studying three
major changes to the ocean caused by climate change: warming,
acidification, and deoxygenation. Both
low oxygen and acidity are expected to worsen as ocean temperatures
rise, especially in areas that already have a history
of naturally low oxygen levels.
Bottom
waters have lower dissolved oxygen levels than at the surface. So
mud-dwelling
organisms like shellfish are
usually the first to suffocate when oxygen levels plummet.
NJ learned that 40 years
ago.
1976
June
is the 40th anniversary of the first reports
by divers off Sandy Hook of a floc-covered seafloor of dead or dying
fish and shellfish. By the 4th
of July, sulfide-blackened
bottom waters had expanded southward about 12
miles off Manasquan (Mahoney, 1979; Walsh, 1979).
By the time the
Bicentennial summer had passed, 3300 square miles of bottom waters -
60 feet to 37 miles offshore, from Sandy Hook to Cape May – had
become hypoxic (low-oxygen) or anoxic (no oxygen) (Sindermann et
al., 1979).
(For maps: see this NMFS
map on NJScuba.net;
as well as pdf-pages 13-22 of “Long-Term
Biological Effects Of Hypoxic Water Conditions Off New Jersey, USA –
1976-1989”.)
Cooler temperatures and
vertical
mixing of the water column finally put oxygen back into the
bottom waters by October. But the commercial fishing industry has
lost more than $430
million in surf clams, bluefish, tuna, fluke, sea bass, and
lobster. It was declared a resource disaster area by the Federal
government, and is still the worst marine die-off in the state’s
recorded history (Sinderman et al., 1979; Walsh, 1979).
Not Pollution
While the die-off happened
near the highly-polluted Hudson-Raritan Estuary, as well as the
sludge and spoils dumpsites that existed offshore in 1976, there jut
wasn't enough nutrients from these sources to account for the scale
of the event (Swanson et al., 1979).
Instead, it was the way
weather and ocean currents came together that year to create an
anomalous, massive event - a "perfect storm”, like
Superstorm
Sandy, but below the ocean surface.
Since it was much warmer
than usual during February and March, the ocean surface began warming
earlier than normal. As the lighter, less dense water at the surface
warmed faster than at the bottom, the water column stratified
and formed a barrier that isolated surface water from bottom water
(Chant et al., 2004a). Salinity (halocline),
temperature (thermocline),and
density (pycnocline)
stratifications
developed earlier than usual (Sinderman et al., 1979; Swanson et
al., 1979). The cooler, denser, and less oxygenated bottom layer
separated from the ocean surface – a few months earlier than
normal.
“ This
meant the trapped oxygen had to last a few months longer.
Secondly, river run off began two months earlier and this led to
more nutrients being deposited into the bay. On top of all of this,
there was significantly less storm action that spring and summer.
Usually the storms break up algae blooms and mix up the water column
bringing oxygen to the deeper water layers. All of this meant the
oxygen in the ocean depths had to last the marine life two additional
months.”
Winds and Currents
Most significantly,
southerly winds began in late winter rather than in April, and
southwest winds persisted for 4-6 weeks through May and June (Malone
et al., 1979; Sinderman et al., 1979; Swanson et al., 1979). Not only
did the wind create a stronger thermocline separating the surface and
bottom water - it concentrated a massive bloom of the dinoflagellate
Ceratium tripos in the isolated bottom waters.
C.
tripos is normally an insignificant species of algae found
offshore in cold, dark water, where its numbers are kept in check by
grazing copepods
(Malone et al., 1979; Sinderman et al., 1979; Swanson et al., 1979).
But that year the southwesterly winds moved it into the sealed-off
bottom waters, where it accumulated from February until July (Malone
et al., 1979; Sinderman et al., 1979; Swanson et al., 1979).
The persistent
southwesterly winds also slowed, then reversed. the normal
southwestward
(north to south) flow of bottom currents on the shelf (Sinderman
et al.,. 1979; Walsh, 1979), massing the algae in stagnating
currents, until the algae bloom finally used up all the available
nutrients and oxygen (Malone et al., 1979; Sinderman et al., 1979;
Swanson et al., 1979). Then the bloom crashed, using up even more
oxygen as it decomposed - initially from Sandy Hook to Manasquan,
then expanding towards Atlantic City (Mahoney, 1979). The dead algae
was the ubiquitous floc the divers had seen.
As the decomposing bloom
rapidly used up all the remaining oxygen, sulfate – the oxygenated
form of sulfur in seawater - was reduced
to the form without oxygen - hydrogen
sulfide. H2S is a gas that smells like rotten eggs
and turns water and mud black. It is lethal to marine life,
especially benthic
(sediment dwelling) organisms – like surf clams, hard shell clams
(quahogs), lobsters, and sea scallops. They are literally stuck in
the mud – and couldn't flee like most of the finfish did. Some of
the territorial fish, such as the eel-like ocean
pout, died hiding in the rocks (Reid, 2006; Sinderman et al.,
1979; Swanson et al., 1979).
Upwellings
The low oxygen event
in 1976 happened in part due to a strong, early upwelling.
Winds normally predominate from the south during the summer in NJ and
form a nearshore
current at the surface that flows to the north. This creates the
littoral
drift that
deposits sand on the southern side of jetties in Monmouth, and is why
we have a barrier beach like Sandy Hook. When southwest winds persist
for several days, cold, higher-saline bottom water flows towards the
shoreline as warmer, lighter water is disperses offshore. Upwellings
are why sometimes on a blazing hot day at the beach the water is too
cold to go swimming.
There
are nice graphics of upwellings at the Rutgers Center for Ocean
Observing Leadership (the COOL Room) here
and here.
In 2015, @Rutgers_Cool tweeted the first
upwelling of the year
on May 26th.
No upwelling tweet so far this year because of our cooler
El Nino spring.
Staying
Tuned
In
2011, Rutgers
tracked chlorophyll
levels in
an offshore algae bloom of Nannochloris
that became huge enough to
make the news
and be called “the blob”. This was also caused
by an upwelling,
and stretched from
Sandy Hook to Cape May,
but was broken
up by Hurricane Irene
in August before it could grow large enough to lower oxygen levels.
Scientists at the Smithsonian
Environmental Research Institute in Maryland have found that
Atlantic
Silversides (spearing) in Chesapeake Bay will die
in oxygen concentrations that don't normally kill them when the water
is also acidic. Silversides are the bottom
of the marine food web in NJ as well. Anything that threatens
their survival also threatens the survival of the larger predator
fish that depend on them.
Rutgers'
Department of Marine and Coastal Sciences uses marine gliders
(Autonomous
Underwater Vehicles) to map subsurface dissolved
oxygen levels off the NJ coast, that has been supported by both
the EPA
and the NJDEP,
Station
JCTN4 (Buoy 126) at the Jacques Cousteau Reserve near Atlantic
City measures dissolved oxygen in the Great Bay at the southern end
of Barnegat Bay.
You
can see which way coastal currents are moving, and lots of other
information, whenever you like, at The
New York Harbor Observing and Prediction System (NYHOPS) webpage,
maintained by the Davidson Laboratory at Stevens Institute of
Technology.
Selected
References
Chant,
R.; Glenn, S.; and Kohut, J. 2004. Flow reversal during upwelling
conditions on the New Jersey inner shelf. Journal of Geophysical
Research. Vol. 109, C12S03.
Figley,
B., Carlson, J., Vaughan, D., and Hollings, S. Accessed 6/5/16. Ocean
Fishkill/1976. NJScuba.net
http://www.njscuba.net/biology/misc_water.php#FishKill
Malone,
T., Esaias, W. and Falkowski, P. 1979. Chapter 9. Plankton dynamics
and nutrient cycling. Part 1. Water column processes. In Oxygen
Depletion and Associated Benthic Mortalities in the New York Bight,
1976. NOAA Professional Paper 11. Rockville Md. December.
Mahoney,
J. 1979. Chapter 9. Plankton dynamics and nutrient cycling. Part 2.
Bloom decomposition. In
Oxygen
Depletion and Associated Benthic Mortalities in the New York Bight,
1976. NOAA Professional Paper 11. Rockville Md. December.
Rutgers
Department of Marine and Coastal Sciences. Accessed 6/5/16. Discover
New Jersey’s Dead Zone
http://marine.rutgers.edu/~sage/BeanCreative/Unit1_Plume/4 Discover
NJ Blooms.doc
Sindermann,
C. and Swanson, L. 1979. Chapter 1. Historical and regional
perspective. In Oxygen
Depletion
and Associated Benthic Mortalities in the New York Bight, 1976. NOAA
Professional Paper 11. Rockville Md. December.
Swanson,
L., Sindermann, C. and Han, G. 1979. Oxygen depletion and the future:
an evaluation. In Oxygen Depletion and Associated Benthic Mortalities
in the New York Bight, 1976. NOAA Professional Paper 11. Rockville
Md. December.
Reid,
R. and Radosh, D. 1979. Benthic Macrofaunal Recovery After the 1976
Hypoxia off,New Jersey
U.
S. Department of Commerce. National Oceanic and Atmospheric
Administration. National Marine Fisheries Service. Northeast
Fisheries Center. Sandy Hook Laboratory Highlands, New Jersey 07732
http://www.nefsc.noaa.gov/publications/series/shlr/shlr79-18.pdf
Walsh,
J. 1979. Forward – Oxygen Depletion and Associated Benthic
Mortalities in the New York Bight, 1976. NOAA Professional Paper 11.
Rockville Md. December.
