Pre-Hurricane CODAR Fields

Here is a quick update on the Mid-Atlantic HF Radar network.  First a look at the 25 hour average surface currents from today overlaid on today’s satellite SST.   This is from our HF Radar viewer website http://marine.rutgers.edu/cool/codar/maracoos/

The surface currents above from the shore based radar line up nicely with the satellite derived temperature fronts, increasing our confidence in each product.  Currents in the vicinity of the New Jersey Bloom remain heading offshore.   That will change with the approach of the hurricane on Saturday.

Below we have the codar surface currents overlaid on the satellite color imagery.  We see the serpentine bloom over the Hudson Shelf Valley, and the offshore face of the front moving southeast.  Glider RU23 is moving west into this layer.

So the CODAR network is up and running.  Better than ever before.  We have more stations deployed and all are turned on.  We suspect there will be power outages and storm damage as the Hurricane passes by on saturday and sunday.  Hopefully the network is spared, and we get one of our best storm datasets ever.  As the storm approaches, the bloom will be hidden under the clouds, some mixing will occur, and we will have to wait for the clouds to clear to see the effect in the satellite data.  The HF radar and gliders will be our eyes during the storm.   Jack Harlan, the leader of the National HF Radar network, has already wished us all good luck through this event.

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REMUS Runs The Bloom

The Rutgers REMUS team was busy yesterday deploying the propeller driven AUV along a cross-shelf transect of the bloom.   The REMUS was tasked on a line just north of RU16′s cross-shelf line.  The exact track is shown below as a series of waypoints (yellow thumbtacks).   The section is through the higher concentrations observed by the satellite remote sensing (shown as a color plot background).

The AUV was sent on a mission to waypoint 8 and then back.   During the mission the AUV undulated throughout the water column measuring temperature, salinity, Chl-a concentration, and dissolved oxygen.

Here is our first cross-section plot of Chl-a concentration associated with this coastal bloom.   Along the line you can see higher concentrations near the coast.   As the REMUS moved offshore, the bloom stays in the surface layer and deepens along the strong thermocline.

Like RU16, the dissolved oxygen observed by the REMUS shows a bimodal structure with higher concentration in the surface layer and lower concentrations in the colder bottom layer.  We want to thank the Rutgers REMUS team for getting the vehicle out quickly in advance of the approaching storm.

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Glider Update

We now have two gliders sampling this bloom.   RU23 seen in the upper right of the map below is transecting west from a deployment off Martha’s Vineyard.   This glider will continue to the west into the lower concentrations associated with the bloom further offshore.  The color overlay on the map is Chl Concentration observed from the MODIS satellite sensor.   Red are higher values and pink are near zero values.

RU16 has been focused on the inshore section of the bloom.   Over the last several days it has transected offshore and back inshore in the highest concentrations seen in the bloom.

Since reaching the the inshore waypoint, ru16 has begun to fly back offshore along the same line.  Our intention with this glider is to capture the cross-shelf variation in dissolved oxygen associated with the bloom.  The glider shows us that the water column is still very stratified with more mixed conditions right near the coast (below).

The above transect shows conditions over the entire mission.   The most recent transects moving offshore and back inshore are seen in the data starting on the 21st of August.

The dissolved oxygen also shows a two layer system with higher concentrations in the surface layer and lower concentrations in the bottom layer, particularly closer to shore.   The distribution of oxygen is seen in a histogram of the last transect showing the bi-modal distribution with surface values (7-8.5 mg/L) and bottom values (3.6 – 5.2 mg/L).

Over the next several days we will position the gliders in the deeper water of the mid-shelf to sample through the forecasted hurricane coming this weekend.  Following the storm the gliders will move inshore to sample the impact of the storm on the bloom and associated dissolved oxygen.

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August 22 Update

Sunday  provided  New Jersey with strong thunder storms and  heavy rains.  So the  question today was if the storm disrupted the bloom and  whether the clouds would clear in time for a nice image. Luckily the clouds were clear by the early afternoon during satellite passes which allowed us to collect new imagery.  The ocean color imagery shows the high chlorophyll bloom remains  along the southern coast of New Jersey.  A significant fraction of high chlorophyll water continues to advect  northward and then alongshore off Long Island.

CODAR current maps (below is the 25 hour average) show the offshore transport of coastal waters from off New Jersey.  These waters likely combine with the southern flowing currents from the Hudson river area; however the extent of the relative contributions of these distinct water masses will require a detailed analysis that will be forthcoming. Currently there is not much temperature variability across the shelf

The glider continues to continue to survey the middle and southern regions of New Jersey.  The nearshore bottom waters show lower percent oxygen saturation values with values around 60%  (oxygen values >3.1).  We will continue to monitor the situation this week.

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Sunday morning and beautiful satellite imagery from Saturday to share

Josh outlined nicely the subsurface features observed by the glider.  We had nice clear sky pictures and we were able to collect some nice satellite imagery which is complemented by the IOOS Codar data.

The phytoplankton bloom continues to be large.  The largest concentrations remain centered off southern New Jersey.  The patch of chlorophyll that detached from the bloom last week continues to be advected north the then directly eastward offshore Long Island.  The concentrations of the offshore patch continues to decrease as it is advected offshore. Peak concentrations of chlorophyll remain high, upwards of 15 mg Chl/m3. 

Some composite HF radar and SST maps are shown below.  The CODAR showed southerly flowing currents along Long Island from the north waters from Massachusetts which is transporting cooler water to the northern regions of the Mid-Atlantic Bight.  You can see the cooler water present in the east Long island sound and along the southern Long Island coast.  Offshore the higher chlorophyll waters appear to be associated with the warmer water. The nearshore currents at the Hudson show recirculation and the main southerly flow appears to originate from the mean flow from the Gulf Maine.  There appears to be upwelling of the mouth of Delaware Bay and southern New Jersey as seen as 22 degree water, in contrast to the offshore water temperatures that are closer to 30 degrees.

 

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Gliding into the Bloom

RU16 has been transecting down the coast since it was deployed on August 13.   The glider’s mission is to support NJDEP and EPA monitoring of coastal dissolved oxygen conditions.  Over the last week, the glider has been transecting back and forth from the shallow nearshore waters to the deep waters offshore.   As the glider moves south we are getting closer to the historic upwelling centers of southern New Jersey that fuel these summer blooms.  Based on input from EPA and NJDEP we will now break the glider from its coastal monitoring mission and focus on the bloom before the glider continues down the coast toward Cape May.   The latest Chl satellite image is shown below.   We can see the higher concentrations associated with the bloom off Little Egg Harbor shown in red.

Over the next couple days the glider is going to head back offshore across the northern edge of the bloom (Waypoint #3).   Once the glider reaches this offshore point, we will send it a bit south (Waypoint #4) so that it can come back inshore along the main axis of the bloom toward waypoint #5.   The glider will then be tasked to go back and forth between waypoints #4 and #5 to track the evolution of the temperature and dissolved oxygen associated with the bloom.

Sub-Surface Temperature

The temperature section from the glider shows a very strong summer thermocline with a warmer surface layer and cold bottom layer.   The last two nearshore waypoints (Seen as the shallow humps in the above plot) have seen reduced stratification with a warmer surface layer over the first and a warmer bottom layer over the second.

Dissolved Oxygen

The dissolved oxygen profiles show a well saturated surface ocean with likely sources from the atmosphere and the large phytoplankton bloom.   Below the thermocline, particulalry further to the south (right on the above plot), the oxygen levels decrease.  Nearshore the oxygen reaches a minimum in the bottom layer.   As the glider heads offshore and more into the center of the bloom we will monitor how this dissolved oxygen field evolves.

 

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Looking back at the SST over the last month does show upwelling!

Given the conflicting opinions yesterday, I thought it might be useful to look back at the ocean temperatures of the last month.  The one unfortunate issue is that it has been cloudy so the coverage of the Mid-Atlantic is spotty. Starting on July 11, the waters over most of the shelf are warm, while possibly some upwelling (indicated by cooler temperatures) at the mouth of Delaware and southern New Jersey there are possibly indications of cooler surface water.

Jumping ahead to July 22, we now see bands of cold water along the New Jersey coast.  This is consistent with model runs that suggested that the upwelling began in earnest the week July 17th.  The image is the backed up by even more intense upwelling observed on the next day.  Note the cold upwelling waters reaches the 20 meter isobath, ~20 kilometers offshore.

That cold water zone increases offshore as seen in the image of July 27th.

By August second, the upwelling appears to have declined however a uniform band of cool water near the coast is still visible.

By August 17, the upwelling continues at a minor level.  The purple up by New York I believe is cloud cover and contamination.

So in brief, we saw in July that upwelling began and then was sustained but albiet in a weaker mode into the month of August. W hat does the ocean color story provide us?  We now look at a series of satellite absorption maps  for the 488 nm wavelength.

Starting on July 7, we see enhanced absorption (proportion to amount of the material in the water)  for the Southern New Jersey and near Delaware Bay.  Enhanced turbid water in the Hudson river is also visible.

These turbid water increase both in the North and in South increase by July 12.  Note the spreading high values near the coast. The mid-shelf streak remains a quandry and will require an analysis of the CODAR currents.  This picture remains consistent through July 16th, but note the 0.1 values now extend further across the shelf.

By the 26th, the blue absorption values of o.1 are observed the over the entire shelf.

By August 6 the bloom is now maturing as the values of 0.1 seen the week before have increased significantly.

The edges of the bloom mature, again the highest values are nearshore in upwelling waters and in Hudson river and Delaware Bay.  However there is no connection of the Hudson river or the Delaware turbid water to the southern New Jersey bloom of material.

By the 17th of August, a major segment of the Southern plume has been advected to the north.  The Hudson river water is visible, yet values are lower then observed for Southern bloom.

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Organizing efforts studying the bloom offshore

The ongoing efforts to understand the dynamics driving and consequences of the massive phytoplankton bloom off the coast of New Jersey can be coordinated at this blog. Feel free to share your input with us and we can post the thoughts.

Josh sent on links to articlea that came out today.
http://www.app.com/article/20110819/NJNEWS/308200004/Algae-bloom-stretches-100-miles-along-Jersey-coast?odyssey=tab|topnews|text|Frontpage

http://www.nj.com/news/index.ssf/2011/08/assive_algae_bloom_off_new_jer.html

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Massive Phytoplankton Bloom in the Mid Atlantic Bight

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Figure1. True Color Satellite Image: August 17, 2011

A large dramatic phytoplankton bloom is occurring in the Mid-Atlantic Bight. These are natural events and phytoplankton form the base of the marine food web. The “bloom” of phytoplankton is almost as large as the state of New Jersey and is easily visible in satellite imagery. These events are driven by ocean circulation patterns and this bloom off southern New Jersey does not appear to be related to outflow from the Hudson river.

Looking at historical data is this biological event large? Yes it is. Figure 2 shows the mean monthly chlorophyll from almost a decade of data (figure is taken from a  Xu et al 2011 {see reference at end of the post }). Chlorophyll is often used to measure the concentration of phytoplankton in the water.

Color Time Series

Figure 2 shows typical chlorophyll concentrations are on average 0.5 to 1.5 mg chlorophyll/m3, but the bloom we are seeing this month is around 15-20 mg chlorophyll/m3 (see Figure 3).

 

Phytoplankton images of MAB

Figure 3 shows the satellite measured map of chlorophyll (colors) and the surface circulation measured by the MARACOOS surface current CODAR network.  The arrows show the direction and speed of the surface currents.  What is visible is that a portion of the bloom detached and is being transported offshore and to the north.

Is this circulation pattern consistent with historical circulation patterns? Yes as we can see in Figure 4.  Figure 4 is taken from a publication by Gong et al. 2010 (see reference below). The first panel shows the average shelf circulation response to southwest wind.  It shows the northward transport consistent with what we have been seeing over the last week. Panel B shows a simulation of how particles would be transported, the particle trajectories show transport to the north and offshore, which is consistent with the satellite images of chlorophyll.

Mean Currents

Figure 4. A: Summer time mean currents in response to southwesterly winds. B: Summer 2006 drifter trajectories in response to southwesterly winds are first offshore and then move back toward the south offshore (Gong, et al, 2010).

What caused this bloom?  Using numerical models of the ocean (check and make your own animations at: http://www.myroms.org/applications/espresso/animations.php

The models suggest that in Mid-July we had a large upwelling event. Upwelling is the wind-driven transport of bottom water in the ocean to the surface. The bottom waters contain nutrients that can support phytoplankton growth. The upwelling is driven by regional patterns, and off the coast of New Jersey this is winds from the southwest. Therefore we believe this event is driven upwelling of ocean bottom water. This is consistent with satellite data that showed low chlorophyll in early July (Figure 5) which shows values starting to increase in mid-July well before the large rains that have resulted in river run-off.

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Figure 5. Map of chlorophyll on July 1

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Figure 6. Map of chlorophyll on July 16

What are the conditions within the bloom? We are using a robot to collect data within the bloom. We are using a autonomous underwater glider that is being controlled by scientists at Rutgers.

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Figure 7. Location of Rutgers webb glider that is surveying along New Jersey. The second panel shows the percent oxygen saturation

The glider shows the surface waters are supersaturated for oxygen. This reflects photosynthesis by the phytoplankton that produces oxygen in the surface where the cells have ample light to grow.  The bottom waters show lower concentrations of oxygen, reflecting the lack of photosynthesis and the respiration by bacteria/animals that live in those waters. Samples collected within the bloom show that it is a mixed community of algae that includes diatoms and dinoflagellates.  The robot will continue monitor condition in the ocean for the next week. You view the data  which updated several time a day. To see the evolving data go to http://marine.rutgers.edu/cool/auvs/index.php?did=221&view=imagery

References:

  • Donglai Gong, Josh T. Kohut,1 and Scott. M. Glenn – Seasonal climatology of wind‐driven circulation on the New Jersey Shelf – JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, C04006, doi:10.1029/2009JC005520, 2010
  • Xu, Y., Chant, R. C., Gong, D., Castaleo, R., Glenn, S. Schofield, O. 2011. Seasonal dynamics in the chlorophyll a in the Mid-Atlantic Bight. Journal of Geophysical Research. Continental Shelf Research. 10.1016/j.csr.2011.05.019
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