**1. Introduction**

Gas hydrate is a solid component (clathrates) composed of water and natural gas of low molecular weight (mainly methane), forming under particular condition of low temperature, high pressure, and proper gas concentration [1]. Pressure and temperature define the stability field of gas hydrate, which is affected by gas mixture and pore-fluids composition (salinity). Moreover, the presence of only a small percentage of higher hydrocarbons (such as ethane and propane) shifts the phase boundary to higher temperature (at constant pressure). Generally, hydrates accumulate anywhere in the ocean-bottom sediments where water depth exceeds about 400 m (**Figure 1**). In Polar Regions, in presence of sub-seawater permafrost, the hydrate could be stable at shallower water as demonstrated recently by [2, 3]. Very deep (abyssal) sediments are generally not thought to house hydrates in large quantities due to the lack of high biologic productivity (necessary to produce the organic matter that is converted to methane) and rapid sedimentation rates (necessary to bury the organic matter), both necessary for hydrate formation on the continental shelves. The conditions for gas hydrate stability are verified also in seawater, but gas concentration is always not sufficient for their formations.

Gas hydrates were discovered in 1810 by Humphry Davy [4] and, since then, they became the interest of scientific and engineering research studies. In fact, the stability of methane hydrates on the sea floor has several implications (i.e., "in [5, 6]"). First, they are considered a huge energy resource (i.e., "in [7]"). Second, natural and anthropogenic disturbances may cause their destabilization causing the

**Figure 1.** *Schematic diagram of the gas hydrate stability zone in marine environment.*

release of huge amounts of fluids (gas and water) and affecting slope stability (i.e., "in [8]"). Finally, methane is an effective greenhouse gas (26 times more powerful than carbon dioxide), and large methane releases may be the cause of sudden episodes of climatic warming in the geologic past (i.e., "in [9]"). Some authors suggested that gas hydrate dissociation influenced significantly climate changes in the late Quaternary period (i.e., "in [10]"). The Clathrate Gun Hypothesis (i.e., "in [11]") suggests that past increases in water temperatures near the seafloor may have induced such a large-scale dissociation, with the methane spike and isotopic anomalies reflected in polar ice cores and in benthic foraminifera [12]. [13] suggested that methane would oxidize fairly quickly in the atmosphere, but could cause enough warming that other mechanisms (for example, release of carbon dioxide from carbonate rocks and decaying biomass) could keep the temperatures elevated.

The relationship between gas hydrate and climate change is of great importance in Polar Regions, where the climate signal is amplified. When pressure and temperature at the sea bottom change (eustatic and climatic changes, respectively), the thickness and the depth of the gas hydrate stability zone change accordingly (i.e., "in [14, 15]"). The study of gas hydrates and the parameters, that control their stability field, allow reconstructing the climatic changes in the past, studying the present processes, and formulating predictions. During the glaciations, the consequent sea level drop produces a rising of the base of the stability field of gas hydrates. This change produces the release of remarkable quantities of methane in the water column, and a sensible continental slope instability, which may cause slides, and, in turn, occasionally tsunami waves. In the other hand, during the interglacial period, the sea level rise and the consequent heating produce an overdeepening of the base of the gas hydrate stability and a progressive accumulation of methane within the

**3**

ture data.

*Gas Hydrates in Antarctica*

ice-sheet wastage.

*DOI: http://dx.doi.org/10.5772/intechopen.94306*

to the global temperature lowering [16].

passive) and in proximity of mud volcanoes (i.e., "in [18]").

gas hydrate zone. Therefore, the climatic changes greatly influence the amounts of methane present in the gas hydrate zone: the release of this gas in the atmosphere during the glaciations influences the interglacial phases, while the decrease of methane content in the atmosphere during the interglacial phases again contributes

Seismic data analysis allow recognizing the presence of gas hydrate in marine environments, because the phase transition (from solid above, to fluid and gasses, below) of interstitial water and gas mixture produces a strong reflection, called Bottom Simulating Reflector (BSR) that simulates the sea bottom and presents a phase reversal with respect to the seafloor reflection. The BSR was firstly discovered and associated to gas hydrate presence in marine sediments in the western Gulf of Mexico, off the northern coasts of Colombia and Panama, and along the Pacific Coast of Central America from Panama to Acapulco by [17]. Successively, in marine environment the BSR was detected along continental margins (both active and

Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon [19]. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. No data exist forrates of methanogenesis in sub-Antarctic marine sediments. [20] presented

experimental data from subglacial environments, similar to Antarctica, that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. They also numerically simulated the accumulation of methane hydrate in Antarctic sedimentary basins and show that pressure/temperature conditions favor methane hydrate formation down to sediment depths of about 300 meters in West Antarctica and 700 meters in East Antarctica. Moreover, [20] calculated that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost, suggesting that he Antarctic Ice Sheet may be an important component of the global methane budget, with the potential to act as a positive feedback on climate warming during

The gas hydrates accumulated in the Antarctic margins could be inferred from geophysical and geochemical evidences, such as BSR on the seismic profile, as already mentioned, high concentrations of methane and organic carbon and abnormal varieties of salinity, chlorinity and sulfate of pore waters in boring sediment samples of Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites. Few potential distributing areas of gas hydrates have been recognized in literature: the South Shetland continental margin, the Weddell Sea, the Ross Sea

In Antarctic margins, there are advantageous geological conditions for the formation and accumulation of gas hydrates according to analysis of the reservoir conditions, including gas source, sedimentation, heat flow, temperature, pressure and tectonic conditions, etc. In fact, the modeling of the theoretical base of the gas hydrate stability points out that there is considerable potential resource of gas hydrate in the Antarctic margins. In particular, [21, 22] modeled the gas hydrate distribution in the South Shetland Margin based on geophysical data, while [23] reconstructed the theoretical depth of the BSR in the Ross Sea based on the litera-

The South Shetland margin (SSM, offshore Antarctic Peninsula) is the most studied part of Antarctica from gas hydrate point of view. In this area, an important gas hydrate reservoir was discovered and was well studied in the recent years with the main purpose to determine the relationship between hydrate stability and

environment effects, including climate change.

continental margin and the Wilkes Land continental margin (**Figure 2**).

#### *Gas Hydrates in Antarctica DOI: http://dx.doi.org/10.5772/intechopen.94306*

*Glaciers and the Polar Environment*

release of huge amounts of fluids (gas and water) and affecting slope stability (i.e., "in [8]"). Finally, methane is an effective greenhouse gas (26 times more powerful than carbon dioxide), and large methane releases may be the cause of sudden episodes of climatic warming in the geologic past (i.e., "in [9]"). Some authors suggested that gas hydrate dissociation influenced significantly climate changes in the late Quaternary period (i.e., "in [10]"). The Clathrate Gun Hypothesis (i.e., "in [11]") suggests that past increases in water temperatures near the seafloor may have induced such a large-scale dissociation, with the methane spike and isotopic anomalies reflected in polar ice cores and in benthic foraminifera [12]. [13] suggested that methane would oxidize fairly quickly in the atmosphere, but could cause enough warming that other mechanisms (for example, release of carbon dioxide from carbonate rocks and decaying biomass) could keep the temperatures elevated. The relationship between gas hydrate and climate change is of great importance in Polar Regions, where the climate signal is amplified. When pressure and temperature at the sea bottom change (eustatic and climatic changes, respectively), the thickness and the depth of the gas hydrate stability zone change accordingly (i.e., "in [14, 15]"). The study of gas hydrates and the parameters, that control their stability field, allow reconstructing the climatic changes in the past, studying the present processes, and formulating predictions. During the glaciations, the consequent sea level drop produces a rising of the base of the stability field of gas hydrates. This change produces the release of remarkable quantities of methane in the water column, and a sensible continental slope instability, which may cause slides, and, in turn, occasionally tsunami waves. In the other hand, during the interglacial period, the sea level rise and the consequent heating produce an overdeepening of the base of the gas hydrate stability and a progressive accumulation of methane within the

*Schematic diagram of the gas hydrate stability zone in marine environment.*

**2**

**Figure 1.**

gas hydrate zone. Therefore, the climatic changes greatly influence the amounts of methane present in the gas hydrate zone: the release of this gas in the atmosphere during the glaciations influences the interglacial phases, while the decrease of methane content in the atmosphere during the interglacial phases again contributes to the global temperature lowering [16].

Seismic data analysis allow recognizing the presence of gas hydrate in marine environments, because the phase transition (from solid above, to fluid and gasses, below) of interstitial water and gas mixture produces a strong reflection, called Bottom Simulating Reflector (BSR) that simulates the sea bottom and presents a phase reversal with respect to the seafloor reflection. The BSR was firstly discovered and associated to gas hydrate presence in marine sediments in the western Gulf of Mexico, off the northern coasts of Colombia and Panama, and along the Pacific Coast of Central America from Panama to Acapulco by [17]. Successively, in marine environment the BSR was detected along continental margins (both active and passive) and in proximity of mud volcanoes (i.e., "in [18]").

Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon [19]. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. No data exist forrates of methanogenesis in sub-Antarctic marine sediments. [20] presented experimental data from subglacial environments, similar to Antarctica, that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. They also numerically simulated the accumulation of methane hydrate in Antarctic sedimentary basins and show that pressure/temperature conditions favor methane hydrate formation down to sediment depths of about 300 meters in West Antarctica and 700 meters in East Antarctica. Moreover, [20] calculated that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost, suggesting that he Antarctic Ice Sheet may be an important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.

The gas hydrates accumulated in the Antarctic margins could be inferred from geophysical and geochemical evidences, such as BSR on the seismic profile, as already mentioned, high concentrations of methane and organic carbon and abnormal varieties of salinity, chlorinity and sulfate of pore waters in boring sediment samples of Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites. Few potential distributing areas of gas hydrates have been recognized in literature: the South Shetland continental margin, the Weddell Sea, the Ross Sea continental margin and the Wilkes Land continental margin (**Figure 2**).

In Antarctic margins, there are advantageous geological conditions for the formation and accumulation of gas hydrates according to analysis of the reservoir conditions, including gas source, sedimentation, heat flow, temperature, pressure and tectonic conditions, etc. In fact, the modeling of the theoretical base of the gas hydrate stability points out that there is considerable potential resource of gas hydrate in the Antarctic margins. In particular, [21, 22] modeled the gas hydrate distribution in the South Shetland Margin based on geophysical data, while [23] reconstructed the theoretical depth of the BSR in the Ross Sea based on the literature data.

The South Shetland margin (SSM, offshore Antarctic Peninsula) is the most studied part of Antarctica from gas hydrate point of view. In this area, an important gas hydrate reservoir was discovered and was well studied in the recent years with the main purpose to determine the relationship between hydrate stability and environment effects, including climate change.

**Figure 2.** *Map of Antarctica showing the potential areas, indicated by points, where there are indication of gas hydrates presence in literature.*
