Less than approximately 10% of the plastic entering the ocean can currently be accounted for, likely due to fragmentation into smallmicroplastics (MP) unquantified by modern techniques or export from the surface ocean. It is not known how much plastic debris actuallyfloats at the ocean surface, what mechanisms control plastic transport and fate from land to the deep sea, and what ecological impact thismay have. The HOTMIC project seeks to address these knowledge gaps by focusing on a model land-ocean linkage between western Europeand the North Atlantic ocean gyre. The objective of HOTMIC is to map the distribution of MP, including particles < 10μm and microfibers, inwater, sediment, and biota from coastal ocean to open ocean gyre to deep sea. This project will quantify processes controlling lateral andvertical transport of MP, including biofouling, (bio)aggregation, and deposition, for incorporation into global ocean models. To understand MPfate in the ocean, HOTMIC will examine microplastic weathering signatures during ocean transport, and evaluate the predominantmechanisms that create the weathering signature, including biological effects of bioshredding and ingestion. These objectives will besupported by a diverse suite of analytical techniques. In order to achieve comprehensive detection of MP particles < 10 μm and microfibers,HOTMIC will develop and optimize novel analytical methods based on a combination of non-destructive (Raman & FT-IR spectrometry,microscopy), and destructive techniques (hydrolytic depolymerization, HPLC, Py-GC/MS, EGA/MS). In addition, HOTMIC will develop Ramanspectroscopy techniques for automated detection of MP incl. particles < 10 μm and microfibers to greatly increase sample throughput, and2D and 3D imaging of MP in biota. HOTMIC will use field and experimental measurements to understand transport and fate of small MP andmicrofibers, and to evaluate the risks of these contaminants for marine environments and organisms.