162
9.3 Ocean Fertilization and Marine N 2 Fixation
Several decades ago, ocean fertilization was proposed as a potential means of compensating for atmospheric CO 2 increases (Martin 1990, 1991). Iron, a trace nutrient,
is in very short supply through large areas of the equatorial and sub-Arctic and subAntarctic oceans referred to as High Nutrient/ Low Chlorophyll (HNLC) regions.
Direct fertilization of some of these regions with soluble Fe have shown stimulation
of primary production and flux of organic C to depth (Boyd et al. 2007; Yoon
et al. 2018).
As noted in Chaps. 7 and 8, Fe can also be in very short supply in Low Nutrient/
Low Chlorophyll (LNLC) regions such as the South Pacific (Bonnet et al. 2008) and
Atlantic (Moore et al. 2009) gyres which may constrain N 2 fixation in these areas.
Indeed, one open ocean Fe + PO 4
-3
experiment attempted to stimulate N 2 fixation in
the subtropical north-east Atlantic but saw no discernable effect on N 2 fixation (as
noted in Boyd et al. 2007; Yoon et al. 2018).
As atmospheric CO 2 levels continue to climb (Jiang et al. 2019), there appears to
be a renewed interest in open ocean fertilization as one means of mitigating the
broader effects of this rise (Yoon et al. 2018) and Fe or dust additions in LNLC
regions may be one target for future consideration, albeit with careful assessment of
the dangers (Emerson 2019). However, the cumulative evidence from open ocean
Fe enrichment studies to date indicate that C export and sequestration is not always
observed (Boyd et al. 2007; Yoon et al. 2018). Modeling efforts suggest that any
export that does occur will likely be reventilated on relatively short time scales
(Aumont and Bopp 2006; Denman 2008; Robinson et al. 2014). Moreover, there is
the possibility of unintended consequences such as the development of sub- euphotic
zone hypoxia and the production of other more potent greenhouse gases (Denman
2008; Furhman and Capone 1991; Oschlies et al. 2010).
9.4 Marine Aquaculture, Biotechnology and N 2 Fixation
Marine microbes have been mined for many novel compounds and biotechnological
applications (Lauritano and Ianora 2018). For instance, a thermostable Taq polymerase from a hot vent Archaea (Neuner et al. 1990) is commercially available and
widely used. In a more relevant vein to this book, a hyperthermal diazotrophic
Archaea has been isolated (Mehta and Baross 2006) and could be a resource for
developing more efficient and economic means of industrial N 2 fixation compared
to the Haber-Bosch process, which requires high temperature (400–500 °C) and
pressure (10 MPa) and which consumes more than 1% of global energy production
(Smil 2001). A biologically based process could also potentially be coupled to the
natural production of H 2 by nitrogenase.
On land, root-nodule rhizobial diazotrophs are an integral component of terrestrial agriculture of leguminous crops (Valentine et al. 2018). With the burgeoning
9 Marine N 2 Fixation, Global Change and the Future
9.3 Ocean Fertilization and Marine N 2 Fixation
Several decades ago, ocean fertilization was proposed as a potential means of compensating for atmospheric CO 2 increases (Martin 1990, 1991). Iron, a trace nutrient,
is in very short supply through large areas of the equatorial and sub-Arctic and subAntarctic oceans referred to as High Nutrient/ Low Chlorophyll (HNLC) regions.
Direct fertilization of some of these regions with soluble Fe have shown stimulation
of primary production and flux of organic C to depth (Boyd et al. 2007; Yoon
et al. 2018).
As noted in Chaps. 7 and 8, Fe can also be in very short supply in Low Nutrient/
Low Chlorophyll (LNLC) regions such as the South Pacific (Bonnet et al. 2008) and
Atlantic (Moore et al. 2009) gyres which may constrain N 2 fixation in these areas.
Indeed, one open ocean Fe + PO 4
-3
experiment attempted to stimulate N 2 fixation in
the subtropical north-east Atlantic but saw no discernable effect on N 2 fixation (as
noted in Boyd et al. 2007; Yoon et al. 2018).
As atmospheric CO 2 levels continue to climb (Jiang et al. 2019), there appears to
be a renewed interest in open ocean fertilization as one means of mitigating the
broader effects of this rise (Yoon et al. 2018) and Fe or dust additions in LNLC
regions may be one target for future consideration, albeit with careful assessment of
the dangers (Emerson 2019). However, the cumulative evidence from open ocean
Fe enrichment studies to date indicate that C export and sequestration is not always
observed (Boyd et al. 2007; Yoon et al. 2018). Modeling efforts suggest that any
export that does occur will likely be reventilated on relatively short time scales
(Aumont and Bopp 2006; Denman 2008; Robinson et al. 2014). Moreover, there is
the possibility of unintended consequences such as the development of sub- euphotic
zone hypoxia and the production of other more potent greenhouse gases (Denman
2008; Furhman and Capone 1991; Oschlies et al. 2010).
9.4 Marine Aquaculture, Biotechnology and N 2 Fixation
Marine microbes have been mined for many novel compounds and biotechnological
applications (Lauritano and Ianora 2018). For instance, a thermostable Taq polymerase from a hot vent Archaea (Neuner et al. 1990) is commercially available and
widely used. In a more relevant vein to this book, a hyperthermal diazotrophic
Archaea has been isolated (Mehta and Baross 2006) and could be a resource for
developing more efficient and economic means of industrial N 2 fixation compared
to the Haber-Bosch process, which requires high temperature (400–500 °C) and
pressure (10 MPa) and which consumes more than 1% of global energy production
(Smil 2001). A biologically based process could also potentially be coupled to the
natural production of H 2 by nitrogenase.
On land, root-nodule rhizobial diazotrophs are an integral component of terrestrial agriculture of leguminous crops (Valentine et al. 2018). With the burgeoning
9 Marine N 2 Fixation, Global Change and the Future