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2006 Shelfwide Cruise: July 20 - July 28

The Issue. The scientific work for the commonly name Dead Zone' is hypoxia or low oxygen. The second largest zone of hypoxia in the world's coastal waters is found int eh Gulf of Mexico adjacent to the Mississippi River system. Important commercial and recreational fisheries are impacted as reduced oxygen levels force fish, shrimp and crabs from the area. Animals that cannot move away die. Freshwater and nutrients from the Mississippi lead to the annual formation of the hypoxic waters, and increasing nutrient loads beginning in the 1950s are responsible for the worsening oxygen conditions since then.

Daily Log

Jul 20, 2006 - Day 0
1900 -  
Prep for cruise, Happy Birthday Melissa
Jul 21, 2006 - Day 1
0010 -  
Depart Cocodrie on R/V Pelican
1000 -  
Arrive Southwest Pass, Mississippi River

Calm, hot, isolated thundershowers

1300 -  
Complete water sampling in Mississippi River

Collection of salinity gradient/nutrient concentrations

Collection of Miss R end member for methyl mercury study

1400 -  
Deploy towed ADCP
1500 -  
Begin hydrographic stations on transect A' and on to transect

Extremely low oxygen levels in bottom waters within the 20- to 25-m isobath

Portunid crabs at water surface over hypoxic bottom waters

High phytoplankton biomass and supersaturated surface waters (>200%)

Mercury methylation box core station

2400 -  
Complete 2 box core stations on transect A
Jul 22, 2006 - Day 2
Calm, slight chop, isolated thundershowers
0200 -  
Complete box core station on transect A
0800 -  
Complete transect A and steam to transect B, LUMCON Fourchon camp on the horizon
1800 -  
Complete transect B

Hypoxic bottom-waters from 5 to 30 m depth

Seas reaching to 2 ft, occasional 3 ft, 9 to 15 kn winds SSW, slowed speed for towed ADCP

Several super tankers at the LOOP (Louisiana Offshore Oil Port) facility

1900 -  
Begin transect C

Spinner sharks!!! Juvenile flying fish!!!

Series of box cores at multiple stations on transect C for microphytobenthos

Portunid crabs at the water surface over bottom water with low oxygen.

Jul 23, 2006 - Day 3
0100 -  
Tow for bulk plankton mercury and methyl mercury determination
0300 -  
Station C6C, site of moored instruments. No diving. Night dives are for the Caribbean, not Gulf of Mexico oil platforms.
0800 -  
Winds 15 kn SSW, choppy
0900 -  
Complete box core series for transect C
1100 -  
Return to C6C to dive and exchange oxygen meter. Frontal passage and squalls as we prepared to dive. Winds 15 kn from the north and building seas. Aborted.
1200 -  
Begin transect D'
1930 -  
Finish transect D' and head west to southern end of transect D.

Extensive hypoxia along transect D' to a depth of 35+ m. Value in 42 m was < 3 mg/L. Most of the afternoon in transit was spent outrunning the front as we headed south finishing the station before the frontal margin reached us. Winds 12-15 kn from the SSW then the SSE.

2100 -  
Begin transect D, complete box coring at D3

Continued low oxygen along this transect.

Where values between 1 to 2 mg/L, dense population of centric diatom Coccinodiscus on chlorophyll filters

Sediment surface at D3 covered with pinnate diatoms

Jul 24, 2006 - Day 4
0700 -  
Complete transect D nearshore, head west to E1

Hypoxia very close to shore, Isle Dernieres

Stalled frontal system, 13 kn SSW, 3 ft swells

1800 -  
Complete transect E, box coring at E2A by the u2018Bu2019 team and E6 by Senn.
2000 -  
Begin transect F, offshore

Box core at deepest station, 40 m, Senn

Continuation of hypoxia in mid to deeper depths

Stalled frontal system turns into 20 kn winds with 4 to 5 ft swells as a tropical depression forms in the southwestern Gulf of Mexico. Watching this as closely as the CTD profiles.

Jul 25, 2006 - Day 5
Happy Birthday Kyle!
0200 -  
Box core F3

Pennate diatoms across the sediment surface, evidence of oxidized Fe, Terrebellid and Ampharetid worms at sediment surface, alive but in 0.3 mg/L oxygen

0600 -  
Complete transect F

Seas calm after F3, but before were quite high

Lower and near anoxic bottom-waters in the mid depth stations of transect F

Winds at 19 kn from ESE

Ballyhoo in dip net

0800 -  
Begin transect G nearshore, calm but dark clouds to the south in the direction of the low pressure system

Fooled us, seas back to 4 ft with higher swells

More fooling around, seas up to 6 to 8 ft swells, wind 27 to 30 kn

Hypoxia in the mid depth stations of transect G

1700 -  
Head to offshore end of transect H, calm enough to box core H6, Senn

Sea cucumbers and a mud crab in single core

Hypoxia in mid depth stations of transect H, mixed nearshore

Jul 26, 2006 - Day 6
0000 -  
Finish transect H, able to box core at H3
0300 -  
Transit to transect I nearshore

Inshore stations of transects H and I well mixed

0630 -  
More hypoxia at mid depth stations on transect I

More winds, up to 30 kn, more seas, 6 to 8, less words

No box coring on transect I

0900 -  
No map as yet, map-maker exhausted .
1000 -  
Seas up to 10 ft, water column mixed to 15 m, still some hypoxia in approx. 20 m depths
1200 -  
Continue on transect J, seas continue
1700 -  
Able to box core transect J at station 4
1900 -  
Hypoxia at mid depth stations on transect J
Jul 27, 2006 - Day 7
0000 -  
Continue transect J

Continued rough seas

0300 -  
Move west to transect K

No box coring

0500 -  
Hypoxia mid depths on transect K
0700 -  
Transit to offshore end of transect M and approaching Louisiana/Texas border
1000 -  
Close off hypoxic bottom area on M line
1100 -  
Return to transect K and complete box core
1200 -  
Transit to J5 to CTD, transit to I4
1700 -  
Complete box core transect I, several stomatopods (mantis shrimp) in cores, transit to G3
2300 -  
Complete box core transect G, transit to D3
Jul 28, 2006 - Day 8
0500 -  
Box core station D3
0630 -  
Transit to C6C to change oxygen meter at bottom
0930 -  
Dive aborted, dive boat not functional, will try next week
1030 -  
Depart for Cocodrie
1400 -  
Arrive at dock