Martin B. FarleyDept. of Geology & Geography

University of North Carolina at Pembroke

History of the Gulf of Mexico “Dead” Zone

Introduction

Audience: Paleontology Undergraduates

An Overarching Objective: Historical Perspective (has this been going

on all along?)

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

Student Background

Location and Cores

Gravity Core at each location plus

Box Core at MRD05-04

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

Forams for Hypoxia Estimation

Degree of anoxia estimated from percentage of low-oxygen tolerant benthics (PEB index) :Protononion atlanticumEpistominella vitreaBuliminella morgani

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

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

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

MRD05-6 Gravity Core

PEB Index

PE0305-1 Gravity Core

PEB Index

MRD05-4 Gravity Core

PEB Index

MRD05-4 Box Core

Plotted at same depth scale as other cores

PEB Index

MRD05-4 Box Core

Plot Expanded for detail

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

1927 Flood

MRD05-4 Box Core

Candidate for 1927 Flood

Flood—Other Cores