Ice crystal formation in clouds stimulated by marine diatoms

The formation of ice crystals in the atmosphere is often facilitated by the presence of small, airborne particles that serve as a “nucleation” site for the growing crystal. Ice nucleation, with or without airborne particles, plays a large role in cirrus cloud formation. However, airborne particles allow ice crystals form in warmer, mixed-phase clouds that would otherwise have been ice-free.

A recent study published in Nature Geoscience reports that a common planktonic diatom, Thalassiosira pseudonana, can actually serve as a nucleation site for ice crystals. Diatoms are single-celled, marine photosynthetic organisms that are most famous for their often beautiful, glassy, silica-rich shells. They are found worldwide and are particularly abundant in cold, nutrient-rich ocean waters, such as the northern Pacific and Antarctic. Samples of T. pseudonana were exposed to water vapor and a supercooled salt solution under “typical tropospheric conditions” (ie, conditions that diatoms would be exposed to in the region of the atmosphere where cirrus-cloud formation takes place). The researchers found that the presence of diatoms in water allowed ice to form at substantially higher temperatures, and that the rate of ice nucleation in the presence of diatoms was generally rapid.

Thalassiosira pseudonana, a planktonic diatom

Small organisms that they are, the ability of diatoms and possibly other phytoplankton to initiate ice nucleation in clouds may have profound effects on climate. Increased ice crystal production due to diatoms could mean more incoming solar radiation reflected away from the earth by clouds (remember albedo effects?). Thus, diatom fragments in clouds may in fact increase the cooling potential of clouds (clouds are also important climate warmers, the water vapor contained within them is a powerful greenhouse gas).

A warming climate has been linked to changes in diatom populations. Warming is expected to lead to selection for smaller species of diatoms, which could be more easily aerosolized. Furthermore, warming may increase diatom populations due to enhanced ocean nutrient availability and decreased Arctic sea ice cover. These processes would both result in an increased concentration of diatomaceous aerosol material in clouds, leading to increased ice-crystal formation. Tiny glass cells, swept up unwittingly and unwillingly from their oceanic homes, may prove an important climate driver as they build icy shelters in the clouds.

Knopf et al. 2010. Stimulation of ice nucleation by marine diatoms. Nature Geoscience 2: 1037.

Advertisements

4 thoughts on “Ice crystal formation in clouds stimulated by marine diatoms”

  1. What a beautiful image, of the tiny diatoms becoming part of the clouds. And the level of dynamic integration of the sea and the sky never ceases to amaze me.

    Diatoms can be either plants or animals, yes?

    1. As far as I know the word ‘diatom’ encompasses a broad group of single-celled algae. I haven’t heard of any diatoms that are classified as animals, but perhaps if there was a non-photosynthetic type…

    1. This article argues that increased ice formation due to diatom material in the atmosphere will have a cooling effect, due to the increased albedo potential of clouds. Albedo refers to the reflection of incoming solar radiation, and has a cooling effect because it essentially deflects some solar radiation that would otherwise make it to the surface.

      However, diatoms in the ocean could be affected in other, unrelated ways due to global warming. There is a theory that warming will increase wind-driven ocean mixing, leading to increased nutrient upwelling from the deep ocean which could stimulate diatom blooms. I don’t know exactly how this would feed back on the climate system, but give that diatoms are already a principle component of oceanic nutrient cycling, I imagine increases in diatom populations could have profound effects.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s