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![Page 1: Martin B. Farley Dept. of Geology & Geography University of North Carolina at Pembroke History of the Gulf of Mexico “Dead” Zone.](https://reader035.fdocuments.us/reader035/viewer/2022062401/5a4d1b687f8b9ab0599b1d99/html5/thumbnails/1.jpg)
Martin B. FarleyDept. of Geology & Geography
University of North Carolina at Pembroke
History of the Gulf of Mexico “Dead” Zone
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Introduction
Audience: Paleontology Undergraduates
An Overarching Objective: Historical Perspective (has this been going
on all along?)
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Major Objectives
Applying Deep Time method to “Shallow Time”
How Fossils can be Paleoenvironmental Indicators
Interpret Change over Time
Evaluation of Anthropogenic Cause for Modern Hypoxia
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Student Background
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Location and Cores
Gravity Core at each location plus
Box Core at MRD05-04
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Benthic Foram Abundances at 1 cm intervals (gravity cores 1.5-2.4 m; box core 40 cm)
Radiocarbon ages at base of two gravity cores (~ 1000 yrs)
Lead-210 for box core
Nature of Data
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Forams for Hypoxia Estimation
Degree of anoxia estimated from percentage of low-oxygen tolerant benthics (PEB index) :Protononion atlanticumEpistominella vitreaBuliminella morgani
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Initial Student Tasks
Calculate PEB index for each core
Graph datadepth increases downcreate graphs with similar depth ranges and PEB ranges for ease of comparison
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Sample Data File
Benthic foraminiferal data MRD05-04BC
sample depth
midpoint (cm)
Number of Protononi
on atlanticum
Number of Epistominella vitrea
Number of Buliminella morgani
Number of other
foraminifers
Age based on Pb-210
PEB Indexsample
depth (cm)0.5 141 123 41 42 2004 88 0.51.5 116 54 12 113 2001 62 1.52.3 117 117 45 36 1998 89 2.33.5 100 146 68 56 1995 85 3.54.5 105 96 52 48 1992 84 4.55.5 186 140 48 67 1989 85 5.56.5 130 105 30 42 1986 86 6.57.5 124 139 62 56 1983 85 7.58.5 174 93 37 42 1980 88 8.59.5 209 88 48 52 1977 87 9.510.5 167 133 61 49 1974 88 10.5
Calculated Fields
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Interpret PEB index for each cores, relate to location
What does the foram record say about the “dead zone” over the last 1000 years?
What context does this give for hypoxia over the last few decades?
Can you identify a candidate for the anoxia associated with the 1927 Mississippi flood?
Student Questions
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MRD05-6 Gravity Core
PEB Index
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PE0305-1 Gravity Core
PEB Index
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MRD05-4 Gravity Core
PEB Index
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MRD05-4 Box Core
Plotted at same depth scale as other cores
PEB Index
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MRD05-4 Box Core
Plot Expanded for detail
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MRD05-6, outside the modern hypoxia zone, has low PEB
PE0305, on edge of modern hypoxia, has spikes in PEB index with increase in shallowest 15 cm
The MRD05-04 cores are within the modern hypoxia zone: Longer core--low PEB indexes at bottom, spikes upward; striking increase in shallowest 25 cm
Box core -- striking increase in the shallowest 17 cm
Data indicate increase in low-oxygen intensity in youngest record.
Rough Interpretations
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1927 Flood
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MRD05-4 Box Core
Candidate for 1927 Flood
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Flood—Other Cores
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