Effect of Southern Ocean freshwater export on the AMOC using an earth system model with interactive icebergs&#160;
Authors: Ackermann Lars , Rackow Thomas , Gierz Paul , Knorr Gregor , Lohmann Gerrit 
Published: March 2021

&lt;p&gt;&lt;span&gt;Variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC) during the Pleistocene are linked to changes in Southern Ocean surface conditions &lt;/span&gt;&lt;span&gt;(Knorr &amp; Lohmann, 2003)&lt;/span&gt;&lt;span&gt;. The so-called Agulhas Leakage is thought to play a crucial role in this teleconnection, transferring buoyancy anomalies &lt;/span&gt;&lt;span&gt;from the Indian Ocean &lt;/span&gt;&lt;span&gt;to the South Atlantic &lt;/span&gt;&lt;span&gt;(Caley et al., 2011; Marino et al., 2013)&lt;/span&gt;&lt;span&gt;. Proxy data of ice-rafted debris (IRD) suggest &lt;/span&gt;&lt;span&gt;that &lt;/span&gt;&lt;span&gt;icebergs originat&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt;&lt;span&gt; in the Southern Ocean have affected the freshwater balance at the Agulhas Plateau during Pleistocene glacial conditions. &lt;/span&gt;&lt;span&gt;In particular, &lt;/span&gt;&lt;span&gt;p&lt;/span&gt;&lt;span&gt;eaks in IRD were found to precede AMOC slowdowns on a millennial time scale &lt;/span&gt;&lt;span&gt;(Starr et al., 2021)&lt;/span&gt;&lt;span&gt;. However, climate models that were used to study these processes did not include an iceberg component or were not fully coupled. To study the relative role of Agulhas leakage and iceberg freshwater forcing and their likely interactions, we recently developed the atmosphere-ocean-&lt;/span&gt;&lt;span&gt;i&lt;/span&gt;&lt;span&gt;ceberg model AWI-ESM-2.1-IB, &lt;/span&gt;&lt;span&gt;which includes a fully coupled Lagrangian iceberg model (Rackow et al., 201&lt;/span&gt;&lt;span&gt;7&lt;/span&gt;&lt;span&gt;). We present preliminary results for &lt;/span&gt;&lt;span&gt;the Last Glacial Maximum&lt;/span&gt;&lt;span&gt; with iceberg seeding in the so-called iceberg alley, applying a modern-day size distribution.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Caley, T., Giraudeau, J., Malaiz&amp;#233;, B., Rossignol, L., &amp; Pierre, C. (2012). Agulhas leakage as a key process in the modes of Quaternary climate changes. &lt;/span&gt;&lt;span&gt;&lt;em&gt;Proceedings of the National Academy of Sciences&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;&lt;em&gt;109&lt;/em&gt;&lt;/span&gt;&lt;span&gt;(18), 6835-6839, &lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Knorr, G., Lohmann, G. (2003). Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation. &lt;/span&gt;&lt;span&gt;&lt;em&gt;Nature&lt;/em&gt;&lt;/span&gt; &lt;span&gt;424&lt;/span&gt;&lt;span&gt;&lt;strong&gt;, &lt;/strong&gt;&lt;/span&gt;&lt;span&gt;532&amp;#8211;536, https://doi.org/10.1038/nature01855.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Marino, G., Zahn, R., Ziegler, M., Purcell, C., Knorr, G., Hall, I. R., Ziveri, P., and Elderfield, H. (2013). Agulhas salt&amp;#8208;leakage oscillations during abrupt climate changes of the Late Pleistocene, &lt;/span&gt;&lt;span&gt;&lt;em&gt;Paleoceanography&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, 28, 599&amp;#8211; 606, doi:&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Rackow, T., Wesche, C., Timmermann, R., Hellmer, H. H., Juricke, S., &amp; Jung, T. (2017). A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates. &lt;/span&gt;&lt;span&gt;&lt;em&gt;Journal of Geophysical Research: Oceans&lt;/em&gt;&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;&lt;em&gt;122&lt;/em&gt;&lt;/span&gt;&lt;span&gt;(4), 3170-3190, &lt;/span&gt;.&lt;/p&gt;&lt;p&gt;&lt;span&gt;Starr, A., Hall, I.R., Barker, S. &lt;/span&gt;&lt;span&gt;&lt;em&gt;et al. &lt;/em&gt;&lt;/span&gt;&lt;span&gt;(2021)&lt;/span&gt;&lt;span&gt;&lt;em&gt;.&lt;/em&gt;&lt;/span&gt;&lt;span&gt; Antarctic icebergs reorganize ocean circulation during Pleistocene glacials. &lt;/span&gt;&lt;span&gt;&lt;em&gt;Nature&lt;/em&gt;&lt;/span&gt; &lt;span&gt;589&lt;/span&gt;&lt;span&gt;&lt;strong&gt;, &lt;/strong&gt;&lt;/span&gt;&lt;span&gt;236&amp;#8211;241, &lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;