Sandin, S. A., Smith, J. E., DeMartini, E. E., Dinsdale, E. A.,
Donner, S. D., Friedlander, A. M., Konotchick, T., Malay, M.,
Maragos, J. E., Obura, D., Pantos, O., Paulay, G., Richie, M.,
Rohwer, F., Schroeder, R. E., Walsh, S., Jackson, J. B. C.,
Knowlton, N., and Sala, E., 2008. Baselines and degradation of
coral reefs in the Northern Line Islands. PLoS ONE, 3, e1548.
Vega Thurber, R., Willner-Hall, D., Rodriguez-Mueller, B.,
Desnues, C., Edwards, R. A., Angly, F., Dinsdale, E. A.,
Kelly, L., and Rohwer, F., 2009. Metagenomic analysis of
stressed coral holobionts. Environmental Microbiology, 11,
2148–2163.
Wegley, L., Edwards, R., Rodriguez-Brito, B., Liu, H., and Rohwer,
F., 2007. Metagenomic analysis of the microbial community
associated with the coral Porites astreoides. Environmental
Microbiology, 9, 2707–2719.
Wegley, L., Yu, Y. N., Breitbart, M., Casas, V., Kline, D. I., and
Rohwer, F., 2004. Coral-associated Archaea. Marine Ecology
Progress Series, 273, 89–96.
MID HOLOCENE
Sarah Woodroffe
Durham University Science Laboratories, Durham, UK
Definition
The Mid Holocene refers to a period of time between c.
7–5 ka cal BP during which large-scale ice sheet melt
ceased. In regions far from former ice sheets, it was the
first time in the present interglacial that relative sea level
(RSL) reached or passed present levels. The end of ice
sheet melt caused a change from rapidly rising RSL during
the early Holocene (c. 10–7 ka cal BP) to relatively stable
RSL between the mid Holocene and present.
Introduction
The tropical reef environments of the Indo-Pacific and
Atlantic have developed in different ways during the
Holocene. This is due to the different broad-scale relative
sea level (RSL) histories experienced by these two regions
through time, particularly during and since the mid Holocene. It is important to understand how global sea level has
fluctuated during this period in order to understand how
these differences have come about.
The early Holocene period was characterized by a
warming climate, which resulted in the complete melt of
the Laurentide and Fennoscandinavian ice sheets, and
a reduction in the size of the Greenland and Antarctic ice
sheets. This large-scale ice sheet melt caused global sea
level to rise quickly in far-field, low-latitude locations,
which are distant from these ice sheets and are not affected
by glacio-isostatic rebound. The rates of RSL rise in some
far-field locations exceeded 8 mm/yr during the early
Holocene (Sloss et al., 2007). By the mid Holocene, the
majority of this melt had ceased; all North American and
European ice sheets had disappeared, Antarctica was relatively stable, and the Greenland ice sheet had retreated
inside its present margin.
Relative sea level in near and intermediate field locations
record the effects of glacio-isostasy (see Chapter entries
“Glacio-Hydro Isostasy” and “Postglacial Transgression”).
However, these effects can extend to considerable distances, penetrating well into the tropical waters of the equatorial low latitudes. This is especially so for sites in the
Atlantic Ocean which lie within the zone of influence of
the former Laurentide Ice Sheet. It is therefore important
not to assume that all tropical locations with fringing and
barrier reefs lie in far-field locations and are unaffected by
glacio-isostasy; tropical reefs in the Caribbean, for example, are not in the far-field zone, whereas the Indo-Pacific
region is a genuinely far-field location.
Equatorial ocean siphoning and continental
levering
Results of a study combining glacio-isostatic modeling
and RSL observations show that the Caribbean is located
sufficiently close to the former Laurentide ice sheet to
be on its lithospheric forebulge (Milne et al., 2005).
The Laurentide ice sheet depressed the crust over North
America and this caused displacement of the lithosphere
away from the center of load. This caused a rim of crustal
uplift outside of the depressed zone. When the ice sheet
melted, the lithosphere migrated back to the former center
of load and caused the forebulge to collapse. During the
early Holocene, the effects of this process were masked
by rapidly rising sea level caused by ice sheet melt, but
since the mid Holocene this process can be seen in RSL
records from both the forebulge region itself, and further
away in the far-field.
In tectonically stable locations in the Caribbean, RSL
has risen throughout the mid-late Holocene, despite the
end of global ice melt c. 7–5 ka cal BP, because of direct
crustal subsidence caused by forebulge collapse. In contrast, in the Indo-Pacific region RSL has fallen by
a small amount (c. 1–2 m) in the late Holocene, as water
has moved from the far-field regions back into space
created by crustal subsidence in the forebulge region.
This process is known as equatorial ocean siphoning
(Mitrovica and Peltier, 1991).
A second process that may be as important as equatorial
ocean siphoning in explaining late Holocene RSL fall in
the Indo-Pacific region is continental levering. As the
underwater shelves around continents were progressively
flooded under rising sea level during the early Holocene,
they subsided under the increased weight of water on
them. Water from the center of large ocean basins (e.g.
Indian and Pacific Oceans) flooded into the space created
by these subsiding shelves, causing RSL to fall in the center of these ocean basins. Model results suggest that RSL
fall in these locations comprises c. 60% due to forebulge
collapse and 40% due to offshore subsidence around continental margins (Mitrovica and Milne, 2002).
Effects on reef development
Reef development differences between the Caribbean
(forebulge zone) and the Indo-Pacific (far-field), and within
698
MID HOLOCENE
Donner, S. D., Friedlander, A. M., Konotchick, T., Malay, M.,
Maragos, J. E., Obura, D., Pantos, O., Paulay, G., Richie, M.,
Rohwer, F., Schroeder, R. E., Walsh, S., Jackson, J. B. C.,
Knowlton, N., and Sala, E., 2008. Baselines and degradation of
coral reefs in the Northern Line Islands. PLoS ONE, 3, e1548.
Vega Thurber, R., Willner-Hall, D., Rodriguez-Mueller, B.,
Desnues, C., Edwards, R. A., Angly, F., Dinsdale, E. A.,
Kelly, L., and Rohwer, F., 2009. Metagenomic analysis of
stressed coral holobionts. Environmental Microbiology, 11,
2148–2163.
Wegley, L., Edwards, R., Rodriguez-Brito, B., Liu, H., and Rohwer,
F., 2007. Metagenomic analysis of the microbial community
associated with the coral Porites astreoides. Environmental
Microbiology, 9, 2707–2719.
Wegley, L., Yu, Y. N., Breitbart, M., Casas, V., Kline, D. I., and
Rohwer, F., 2004. Coral-associated Archaea. Marine Ecology
Progress Series, 273, 89–96.
MID HOLOCENE
Sarah Woodroffe
Durham University Science Laboratories, Durham, UK
Definition
The Mid Holocene refers to a period of time between c.
7–5 ka cal BP during which large-scale ice sheet melt
ceased. In regions far from former ice sheets, it was the
first time in the present interglacial that relative sea level
(RSL) reached or passed present levels. The end of ice
sheet melt caused a change from rapidly rising RSL during
the early Holocene (c. 10–7 ka cal BP) to relatively stable
RSL between the mid Holocene and present.
Introduction
The tropical reef environments of the Indo-Pacific and
Atlantic have developed in different ways during the
Holocene. This is due to the different broad-scale relative
sea level (RSL) histories experienced by these two regions
through time, particularly during and since the mid Holocene. It is important to understand how global sea level has
fluctuated during this period in order to understand how
these differences have come about.
The early Holocene period was characterized by a
warming climate, which resulted in the complete melt of
the Laurentide and Fennoscandinavian ice sheets, and
a reduction in the size of the Greenland and Antarctic ice
sheets. This large-scale ice sheet melt caused global sea
level to rise quickly in far-field, low-latitude locations,
which are distant from these ice sheets and are not affected
by glacio-isostatic rebound. The rates of RSL rise in some
far-field locations exceeded 8 mm/yr during the early
Holocene (Sloss et al., 2007). By the mid Holocene, the
majority of this melt had ceased; all North American and
European ice sheets had disappeared, Antarctica was relatively stable, and the Greenland ice sheet had retreated
inside its present margin.
Relative sea level in near and intermediate field locations
record the effects of glacio-isostasy (see Chapter entries
“Glacio-Hydro Isostasy” and “Postglacial Transgression”).
However, these effects can extend to considerable distances, penetrating well into the tropical waters of the equatorial low latitudes. This is especially so for sites in the
Atlantic Ocean which lie within the zone of influence of
the former Laurentide Ice Sheet. It is therefore important
not to assume that all tropical locations with fringing and
barrier reefs lie in far-field locations and are unaffected by
glacio-isostasy; tropical reefs in the Caribbean, for example, are not in the far-field zone, whereas the Indo-Pacific
region is a genuinely far-field location.
Equatorial ocean siphoning and continental
levering
Results of a study combining glacio-isostatic modeling
and RSL observations show that the Caribbean is located
sufficiently close to the former Laurentide ice sheet to
be on its lithospheric forebulge (Milne et al., 2005).
The Laurentide ice sheet depressed the crust over North
America and this caused displacement of the lithosphere
away from the center of load. This caused a rim of crustal
uplift outside of the depressed zone. When the ice sheet
melted, the lithosphere migrated back to the former center
of load and caused the forebulge to collapse. During the
early Holocene, the effects of this process were masked
by rapidly rising sea level caused by ice sheet melt, but
since the mid Holocene this process can be seen in RSL
records from both the forebulge region itself, and further
away in the far-field.
In tectonically stable locations in the Caribbean, RSL
has risen throughout the mid-late Holocene, despite the
end of global ice melt c. 7–5 ka cal BP, because of direct
crustal subsidence caused by forebulge collapse. In contrast, in the Indo-Pacific region RSL has fallen by
a small amount (c. 1–2 m) in the late Holocene, as water
has moved from the far-field regions back into space
created by crustal subsidence in the forebulge region.
This process is known as equatorial ocean siphoning
(Mitrovica and Peltier, 1991).
A second process that may be as important as equatorial
ocean siphoning in explaining late Holocene RSL fall in
the Indo-Pacific region is continental levering. As the
underwater shelves around continents were progressively
flooded under rising sea level during the early Holocene,
they subsided under the increased weight of water on
them. Water from the center of large ocean basins (e.g.
Indian and Pacific Oceans) flooded into the space created
by these subsiding shelves, causing RSL to fall in the center of these ocean basins. Model results suggest that RSL
fall in these locations comprises c. 60% due to forebulge
collapse and 40% due to offshore subsidence around continental margins (Mitrovica and Milne, 2002).
Effects on reef development
Reef development differences between the Caribbean
(forebulge zone) and the Indo-Pacific (far-field), and within
698
MID HOLOCENE