81
5.9 Remote Sensing
The vast expanse and dynamic nature of the oceans means that the oceans are chronically undersampled by traditional means of sampling e.g. on oceanographic cruises.
This is particularly true for N 2 fixation, that itself is highly variable in space and time.
Remote sensing using satellites and airborne sensors have provided large scale
information on characteristics of the ocean such as temperature (Minnett et al.
2019), salinity (Dinnat and Yin 2019), sea surface height (Archer et al. 2020), and
even derived nutrients (Goes et al. 1999, 2000). Direct inferences about these characteristics are generally limited to the near surface of the ocean or what is often
referred to as the first optical depth (McClain 2009).
The chlorophyll pigment signature of marine microalgae (including cyanobacteria) has been most effectively exploited to detail seasonal and spatial trends of the
density of these populations in the surface oceans of the world (McClain 2009).
These include estimates of their contribution to primary production (Behrenfeld and
Falkowski 1997).
There are few characteristics of most N 2 -fixing microorganisms that can be
detected remotely. However, the non-heterocyst-forming cyanobacterium
Trichodesmium has two optical properties which allow for its unique detection. It
contains the photosynthetic accessory pigment phycoerythrin which can be distinguished from chlorophyll as well as gas vesicles, proteinaceous bodies which give
it buoyancy and which also impart a high reflectance (Hu et al. 2010; Subramaniam
et al. 1999a, b; Westberry et al. 2005). Trichodesmium is also known to form large
surface blooms or slicks which are readily observable from space (Fig. 4.3b)
(Blondeau-Patissier et al. 2018; McKinna 2015). Large summer blooms of the heterocyst-forming cyanobacterium Nodularia are also easily viewed from satellite
platforms and the International Space Station (Fig. 4.3a).
The ability to deploy instrumentation that can collect data and samples has revolutionized oceanography as well. Moored instruments and autonomous vehicles
have provided the ability to acquire samples and in some cases, such as the
Environmental Sample Processor (ESP) (Preston et al. 2009), can analyze samples
at sea by hybridization or qPCR and remotely transmit the results to shore (Preston
et al. 2009; Scholin et al. 2009). The ESP was deployed to drift and collect
Lagrangian samples which showed the pattern of N 2 -fixing microorganisms along
the gradient between two eddies (Robidart et al. 2014). Remotely deployed drones
with cameras and optical spectrometers are also rapidly entering the field (Zappa
et al. 2020) (Fig. 5.7).
A Robotic Cartridge Sampling Instrument (RoCSI) was recently deployed on a
cruise to filter samples with high spatial resolution collected underway from a
TowFish for analysis of nifH amplicons, expression, qPCR, as well as for pstS P
stress genes (Tang et al. 2020).
5.9 Remote Sensing
5.9 Remote Sensing
The vast expanse and dynamic nature of the oceans means that the oceans are chronically undersampled by traditional means of sampling e.g. on oceanographic cruises.
This is particularly true for N 2 fixation, that itself is highly variable in space and time.
Remote sensing using satellites and airborne sensors have provided large scale
information on characteristics of the ocean such as temperature (Minnett et al.
2019), salinity (Dinnat and Yin 2019), sea surface height (Archer et al. 2020), and
even derived nutrients (Goes et al. 1999, 2000). Direct inferences about these characteristics are generally limited to the near surface of the ocean or what is often
referred to as the first optical depth (McClain 2009).
The chlorophyll pigment signature of marine microalgae (including cyanobacteria) has been most effectively exploited to detail seasonal and spatial trends of the
density of these populations in the surface oceans of the world (McClain 2009).
These include estimates of their contribution to primary production (Behrenfeld and
Falkowski 1997).
There are few characteristics of most N 2 -fixing microorganisms that can be
detected remotely. However, the non-heterocyst-forming cyanobacterium
Trichodesmium has two optical properties which allow for its unique detection. It
contains the photosynthetic accessory pigment phycoerythrin which can be distinguished from chlorophyll as well as gas vesicles, proteinaceous bodies which give
it buoyancy and which also impart a high reflectance (Hu et al. 2010; Subramaniam
et al. 1999a, b; Westberry et al. 2005). Trichodesmium is also known to form large
surface blooms or slicks which are readily observable from space (Fig. 4.3b)
(Blondeau-Patissier et al. 2018; McKinna 2015). Large summer blooms of the heterocyst-forming cyanobacterium Nodularia are also easily viewed from satellite
platforms and the International Space Station (Fig. 4.3a).
The ability to deploy instrumentation that can collect data and samples has revolutionized oceanography as well. Moored instruments and autonomous vehicles
have provided the ability to acquire samples and in some cases, such as the
Environmental Sample Processor (ESP) (Preston et al. 2009), can analyze samples
at sea by hybridization or qPCR and remotely transmit the results to shore (Preston
et al. 2009; Scholin et al. 2009). The ESP was deployed to drift and collect
Lagrangian samples which showed the pattern of N 2 -fixing microorganisms along
the gradient between two eddies (Robidart et al. 2014). Remotely deployed drones
with cameras and optical spectrometers are also rapidly entering the field (Zappa
et al. 2020) (Fig. 5.7).
A Robotic Cartridge Sampling Instrument (RoCSI) was recently deployed on a
cruise to filter samples with high spatial resolution collected underway from a
TowFish for analysis of nifH amplicons, expression, qPCR, as well as for pstS P
stress genes (Tang et al. 2020).
5.9 Remote Sensing