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<p class=MsoNormal><i><span style='font-family:"Arial","sans-serif"'>Nature </span></i><span
class=visually-hidden><b><span style='font-family:"Arial","sans-serif"'>volume</span></b></span><b><span
style='font-family:"Arial","sans-serif"'> 556</span></b><span
style='font-family:"Arial","sans-serif"'>, <span class=visually-hidden>pages</span>497–500<span
class=apple-converted-space> </span>(2018)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>doi:10.1038/s41586-018-0044-z<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-family:"Arial","sans-serif";color:#666666'>Published:
</span><span style='font-family:"Arial","sans-serif"'>18 April 2018<o:p></o:p></span></p>
<h1 style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:10.5pt;
margin-left:0in'><span style='font-family:"Times","serif";font-weight:normal'><o:p> </o:p></span></h1>
<h1 style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:10.5pt;
margin-left:0in'><span style='font-family:"Arial","sans-serif";font-weight:
normal'>Vertically migrating swimmers generate aggregation-scale eddies in a
stratified column<o:p></o:p></span></h1>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-family:"Arial","sans-serif"'><a
href="https://www.nature.com/articles/s41586-018-0044-z?spMailingID=56435783&spUserID=MjA1NTE2ODQxMAS2&spJobID=1382845054&spReportId=MTM4Mjg0NTA1NAS2#auth-1"><span
style='color:windowtext;text-decoration:none'>Isabel A. Houghton</span></a>,<span
class=apple-converted-space> </span><a
href="https://www.nature.com/articles/s41586-018-0044-z?spMailingID=56435783&spUserID=MjA1NTE2ODQxMAS2&spJobID=1382845054&spReportId=MTM4Mjg0NTA1NAS2#auth-2"><span
style='color:windowtext;text-decoration:none'>Jeffrey R. Koseff</span></a>,<span
class=apple-converted-space> </span><a
href="https://www.nature.com/articles/s41586-018-0044-z?spMailingID=56435783&spUserID=MjA1NTE2ODQxMAS2&spJobID=1382845054&spReportId=MTM4Mjg0NTA1NAS2#auth-3"><span
style='color:windowtext;text-decoration:none'>Stephen G. Monismith</span></a><span
class=apple-converted-space> </span>&<span
class=apple-converted-space> </span><a
href="https://www.nature.com/articles/s41586-018-0044-z?spMailingID=56435783&spUserID=MjA1NTE2ODQxMAS2&spJobID=1382845054&spReportId=MTM4Mjg0NTA1NAS2#auth-4"><span
style='color:windowtext;text-decoration:none'>John O. Dabiri</span></a><o:p></o:p></span></p>
<h2 style='mso-margin-top-alt:10.5pt;margin-right:0in;margin-bottom:21.0pt;
margin-left:0in;background:#EEEEEE'><span style='font-family:"Arial","sans-serif";
color:#222222;letter-spacing:.15pt'>Abstract<o:p></o:p></span></h2>
<p style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:21.0pt;
margin-left:0in;line-height:22.45pt;background:white;word-wrap: break-word'><span
style='font-size:13.0pt;font-family:"Arial","sans-serif";color:#222222;
letter-spacing:.15pt'>Biologically generated turbulence has been proposed as an
important contributor to nutrient transport and ocean mixing</span><sup><span
style='font-size:9.5pt;font-family:"Arial","sans-serif";color:#222222;
letter-spacing:.15pt'><a
href="https://www.nature.com/articles/s41586-018-0044-z?spMailingID=56435783&spUserID=MjA1NTE2ODQxMAS2&spJobID=1382845054&spReportId=MTM4Mjg0NTA1NAS2#ref-CR1"
title="Dewar, W. K. et al. Does the marine biosphere mix the ocean? J. Mar. Res. 64, 541–561 (2006)."
id=ref-link-section-d1839e380><span style='color:#006699;text-decoration:none;
vertical-align:baseline'>1</span></a>,<a
href="https://www.nature.com/articles/s41586-018-0044-z?spMailingID=56435783&spUserID=MjA1NTE2ODQxMAS2&spJobID=1382845054&spReportId=MTM4Mjg0NTA1NAS2#ref-CR2"
title="Katija, K. & Dabiri, J. O. A viscosity-enhanced mechanism for biogenic ocean mixing. Nature 460, 624–626 (2009)."
id="ref-link-section-d1839e380_1"><span style='color:#006699;text-decoration:
none;vertical-align:baseline'>2</span></a>,<a
href="https://www.nature.com/articles/s41586-018-0044-z#ref-CR3"
title="Huntley, M. E. & Zhou, M. Influence of animals on turbulence in the sea. Mar. Ecol. Prog. Ser. 273, 65–79 (2004)."
id=ref-link-section-d1839e383><span style='color:#006699;text-decoration:none;
vertical-align:baseline'>3</span></a></span></sup><span style='font-size:13.0pt;
font-family:"Arial","sans-serif";color:#222222;letter-spacing:.15pt'>. However,
to produce non-negligible transport and mixing, such turbulence must produce
eddies at scales comparable to the length scales of stratification in the
ocean. It has previously been argued that biologically generated turbulence is
limited to the scale of the individual animals involved</span><sup><span
style='font-size:9.5pt;font-family:"Arial","sans-serif";color:#222222;
letter-spacing:.15pt'><a
href="https://www.nature.com/articles/s41586-018-0044-z#ref-CR4"
title="Visser, A. W. Biomixing of the oceans? Science 316, 838–839 (2007)."
id=ref-link-section-d1839e387><span style='color:#006699;text-decoration:none;
vertical-align:baseline'>4</span></a></span></sup><span style='font-size:13.0pt;
font-family:"Arial","sans-serif";color:#222222;letter-spacing:.15pt'>, which
would make turbulence created by highly abundant centimetre-scale zooplankton
such as krill irrelevant to ocean mixing. Their small size notwithstanding,
zooplankton form dense aggregations tens of metres in vertical extent as they
undergo diurnal vertical migration over hundreds of metres</span><sup><span
style='font-size:9.5pt;font-family:"Arial","sans-serif";color:#222222;
letter-spacing:.15pt'><a
href="https://www.nature.com/articles/s41586-018-0044-z#ref-CR3"
title="Huntley, M. E. & Zhou, M. Influence of animals on turbulence in the sea. Mar. Ecol. Prog. Ser. 273, 65–79 (2004)."
id=ref-link-section-d1839e391><span style='color:#006699;text-decoration:none;
vertical-align:baseline'>3</span></a>,<a
href="https://www.nature.com/articles/s41586-018-0044-z#ref-CR5"
title="Sato, M., Dower, J. F., Kunze, E. & Dewey, R. Second-order seasonal variability in diel vertical migration timing of euphausiids in a coastal inlet. Mar. Ecol. Prog. Ser. 480, 39–56 (2013)."
id=ref-link-section-d1839e394><span style='color:#006699;text-decoration:none;
vertical-align:baseline'>5</span></a>,<a
href="https://www.nature.com/articles/s41586-018-0044-z#ref-CR6"
title="Hamner, W. M., Hamner, P. P., Strand, S. W. & Gilmer, R. W. Behavior of antarctic krill, Euphausia superba: chemoreception, feeding, schooling, and molting. Science 220, 433–435 (1983)."
id=ref-link-section-d1839e397><span style='color:#006699;text-decoration:none;
vertical-align:baseline'>6</span></a></span></sup><span style='font-size:13.0pt;
font-family:"Arial","sans-serif";color:#222222;letter-spacing:.15pt'>. This
behaviour potentially introduces additional length scales—such as the
scale of the aggregation—that are of relevance to animal interactions
with the surrounding water column. Here we show that the collective vertical
migration of centimetre-scale swimmers—as represented by the brine shrimp<span
class=apple-converted-space> </span><i>Artemia salina</i>—generates
aggregation-scale eddies that mix a stable density stratification, resulting in
an effective turbulent diffusivity up to three orders of magnitude larger than
the molecular diffusivity of salt. These observed large-scale mixing eddies are
the result of flow in the wakes of the individual organisms coalescing to form
a large-scale downward jet during upward swimming, even in the presence of a
strong density stratification relative to typical values observed in the ocean.
<u>The results illustrate the potential for marine zooplankton to considerably
alter the physical and biogeochemical structure of the water column, with potentially
widespread effects owing to their high abundance in climatically important
regions of the ocean</u></span><sup><span style='font-size:9.5pt;font-family:
"Arial","sans-serif";color:#222222;letter-spacing:.15pt'><a
href="https://www.nature.com/articles/s41586-018-0044-z#ref-CR7"
title="Bianchi, D., Galbraith, E. D., Carozza, D. A., Mislan, K. A. S. & Stock, C. A. Intensification of open-ocean oxygen depletion by vertically migrating animals. Nat. Geosci. 6, 545–548 (2013)."
id=ref-link-section-d1839e404><span style='color:#006699;text-decoration:none;
vertical-align:baseline'>7</span></a></span></sup><span style='font-size:13.0pt;
font-family:"Arial","sans-serif";color:#222222;letter-spacing:.15pt'>.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p>
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